Replacing the Long Side - 265 Glass Tank Repair
I purchased a brand new 265 gallon aquarium that was broken. One of the long panels was cracked. I have since removed it and cleaned the majority of the old silicone from the seams. I will use some toluene (?) to really clean the joints of the glass. My question stems from the method that Perfecto uses to 'set' the glass. 
I called, just for kicks, to see how / if they would repair it. I was answered with "we would not repair it, but replace it with a new one" - if it was under warranty, but it is not. The original purchaser caused the damage therefore - no free fix. I did learn that Perfecto is now using 'spacers' on the larger glass tanks to keep the weight of the glass from pushing all the sealant out while it cures. They could not offer any of these spacers to me. So, I can get the glass, the sealant (100% silicone window & door sealer) - but do I need to worry about these spacers? Will the silicone bead be strong enough to hold all the weight of the panel without squashing it all out?
Now, as for the way to actually set the glass. Should I leave it 'right side up' / normal position, or should I lay it on the back (the non broken long side) and then place the glass on from the top? Any info regarding the procedure will be greatly appreciated!
>> I would keep the tank upright, but upside-down. I would place a tank that size on two or three solid easels. Before you start, take five clamps from a hardware store that will fit the sides of the tank. Measure the span, and mark the width on the clamp. Then put plenty of silicone on the edge of the tank. 
When you set the panel do so at the bottom edge (now on top) first, at a 45 degree angle to start. Then flip the panel down into place. Now use the clamps: one at the top and one at the bottom, tighten them until you have reached your mark. Ideally you will put one in the middle at the bottom seam. 
When the silicone is dried, trim the insides and make a proper bead (you can do this from underneath when the silicone is wet if you have used enough). 
If the tank does not have a center brace I would strongly recommend it. I assume that the tank is eight feet long, so you should install a middle brace (same thickness of glass as the rest of the tank) that spans the middle of at least 12-16". This will prevent the front glass from bowing out too much. Good Luck, Oliver <<
<<Marina's note: I would NOT, I repeat NOT use something as toxic as toluene to clean the glass.  All that is needed is a vinegar/water mixture, and rubbing alcohol to get all oils off.  A set of good straight-edge razors is what is needed to best remove all silicone.>>

Glass Repair
<Hi Steve, MacL here with you today.> I was cruising your wonderful site looking for repair ideas for scratched glass and found none. <That's because glass scratches are pretty much permanent, especially if they are on the inside of the glass. Acrylic can be repaired.>
I am considering repairing my 150 with a razor blade and super glue gel. <I'm assuming you mean you would scrape out the silicon with a razor blade and them glue it back with superglue? My understanding is that this will not work over the long term. That if you can get a bond that eventually it will wear out.> Do you know of anyone that has tried that before? <I know one guy who tried and ended up going back to silicon.>
I purchased Calfo's book on Coral Prop and find it a great source but lacking on Fragging Techniques-I need pictures. <Steve, that book is amazing isn't it? There are a few pictures in there and I'm betting he will be updating soon as well. You might try www.fragexchange.com I know they are adding more and more fragging examples and after IMAC in June will have a lot of good examples.>   Can you suggest a good book?  <I don't know that there is a good book on fragging other than Anthony's book but I'm sure it will be covered shortly.>
Thanks.
Steve

New aquarium repair
I just received a 96x30x30 Starphire aquarium from Inter American. The front and side panels are 1/2 inch Starphire the bottom is 3/4 and the back and Euro- bracing is 5/8 regular glass. The problem is that there are hundreds of bubbles in every seam of the aquarium. The bubbles are large some around an inch long. Inter American said that it was normal to have this many bubbles because the glass is tempered
<?>
and they will not give me a refund. When I fill the tank about halfway the left front seal turns chalk white.
<Not good>
It first turns chalk white only at the bubbles but then I can see the white areas spreading the longer it sits. They told me to let it sit empty for a few weeks to let the silicone harden more and that everything would be fine.
<Umm, the Silicone "hardens"... little... it cures in a day...>
I'm guessing they are just lying to me and this problem will not fix itself. The only seam I have seen turn chalk white is the front left but every seam has hundreds of bubbles even the seams of the Euro- bracing. Can I fix this? I do not have any experience with building or fixing aquariums.
Thanks
<Fixing is difficult... requires cutting out the seals... including between the glass (the only functional seal)... I would be talking with your/their States General Attorneys re the legality of this sale, lack of exchange. Bob Fenner> 
 

60 Hex Sealant Lifting I didn't want to post a public chat because the person that I purchased this tank from and the LFS that assured me it was ok use your site. <Okay> The problem is this: I purchased (for my employer) a used 60 gallon hex, cleaned it up, and immediately filled it up and had it running with a power pump in the basement for about 6 weeks while waiting for our new office to be ready. <Good idea> I then emptied it and brought it to work to set it up. A fellow aquarist pointed out that the seals were yellow and lifting. <Lifting!?> We even found a pinhole sized hole on one seam halfway down one inside seam. (Coincidentally I came across someone in one of your articles that had a pinhole sized leak halfway down with a 60 hex). <Yikes> It seems that I should head off any future problems by cutting off the rough edging and resealing it with aquarium sealant. Needless to say a leak at work would be disastrous. I am, of course, upset that I was sold an aquarium with this potential problem as I was assured by the seller and the LFS that the seals were fine. Is this a real, potential disaster or am I being overly cautious? <Hard to say w/o first-hand observation. Was this tank resealed? Or is this the original?> Is it fixable or should I just try to get my employer's money back? (I am having problems with the canister filter that came with it too.) It was only $150 so I might be better off just giving back my employer the $150 and chalking it up to experience. It is sort of a no win situation...please let me know your thoughts. <I share your concern re the seal... it should NOT show signs of disengaging from the wall... Now, know that the actual silicone in the glass joints is largely non-functional, in that it does not do much to hold the tank together... It's more for protecting the actual between-glass silicone from damage, like from a cleaning (razor) tool... And know that a sixty hex is much better than a 75 or 90... that have the same base dimensions, but are much taller... a sixty is 24 inches in height if memory serves... So... w/o seeing it I am not so/very concerned... and you did test it for six weeks... I would at least have another old-timey aquarist come to the sight and check out what you have... and if you can make them, send along pix of what concerns you. Bob Fenner>

Re: 60 Hex Sealant Lifting Wow.  Did not expect to hear from you personally.  I love your book by the way... Will get pictures to you sometime tomorrow.   <Ahh, look forward to seeing this/these> Thank you so much for your time, Elaine <Welcome. Bob Fenner> Re: 60 Hex Sealant Lifting Attached are some pictures of the inside sealing. Two are of the pin-size hole that I found that does go quite a way in (to the outside sealing).   <I see what you mean... looks like the folks doing this job (and it does look original), were using some old Silicone, and/or doing this work quick on a hot, sticky day... None the less, from what I see I would not be concerned> The outside sealing is clear and looks real good. <Yes> Thank you again for taking the time to help! Elaine <A pleasure. Bob Fenner>

Broken Tank Repair
Hi Bob, Love the site.
I acquired a large 156 gallon with the full black oak base for a relatively small amount. However the drawback was that this tank was in a fish store that a friend worked in. The reason they parted with it was that they were using it for reptiles and one of their employees left a heat lamp resting on the top of the glass which obviously cracked the glass. 
I was hoping you could offer me some advise on my repairs. The sides of the tank have no cracks. The tank is six feet long with about a two foot piece on top right in the middle. This whole piece would have to be replaced. The silicone appears to be in great shape all the way around but I am wondering if I should replace It anyway in case a small sliver of glass might cause me damage. 
The silicone holding the top in place is very hard and not to easy to scrape away. I was hoping you might be able to help me decide how to go about removing the piece to repair it. I know you have to use the right silicone but do you think that would have been all they would have used to secure such a structural piece?
< Carefully remove the plastic trim along the top rim of the tank. I have used single edged razor blade and sharpened putty knife with a little effort it can be removed. With the trim removed, the razorblade can be used to remove the silicon attached to the broken piece. Remove the broken glass and remove as much of the old silicon as you can by shaving glass. Get a new piece of glass that will fit that is the same thickness and silicon it in place with silicon that is made for aquariums.>
I carefully vacuumed up the glass that could possibly have been in the tank. What I am thinking is that I can replace the piece and fill it with water to check for leaks and should be able to drain out any Slivers when I remove the water.
< Sounds like a logical approach.>
I am also wondering if you think the guitar string idea might be the best to use here?
< Don't know what the guitar string method is.>
Also even if they had originally only used silicone do you not think it a good idea to use some epoxy to seam the replacement glass piece back in since this piece never resides below the water level.
< I would replace the glass and use only silicon. It is a structural piece of the aquarium and it needed to keep the front and back pieces from bowing and then breaking. Aquariums are pretty well engineered already so I would recommend to just duplicate what is already there and don't get too fancy on making improvements.>
I also seen online where experts like you recommend sanding the edges when seaming the pieces together however I think it would be safe to skip this stage on this particular piece cause this is not a piece that requires water tightness and the abrasion could be an eyesore
<Only sand the edge of the glass that will come in contact with the silicon to give it better adhesion to the glass and thus making a better bond.>
It is an Oceanic Systems aquarium and I could not afford one of this size any other way so any advice GREATLY appreciated. I have additionally added the Oceanic guys in case they can help answer or assist in my information.
< Oceanic is a quality brand aquarium. I am sure once the piece has been replaced and the repair has been done that you will get years of pleasure from your new aquarium.-Chuck><<Mmm, and do check the thickness of the glass of the rest of this tank... It may have been built with thin material... for herptile use... NOT to be filled with water. BobF>>

Another Cracky One (Cracked Tank Bottom)
Hi I am after a bit of advice.
<<Yes, you're going to get a wee bit more than originally bargained for. First, if you send in more messages, please, use proper capitalization and punctuation. Also, I know for a fact that this specific question has been answered before (by Yours Truly), and should be posted on WWM.>>
Recently while moving house I managed to crack the bottom of my glass tank (48x15x15) and am getting some conflicting advice on how to repair it. I was thinking about using a sheet of Perspex to cover the crack but have been told that this will not work as the silicone will not bond the glass to silicon. 
<<I have no idea what Perspex is.. <Googling, processing..>... AHA! It's sort of like Plexiglas.>>
Is this true or should I use a sheet of glass to repair it your advice would be appreciated, Thanks Les
<<Yes, this is true. New silicone will not bond to old, will not bond to plastics, glass only. Seek the wisdom already posted on WWM on how to make this repair. Marina>>

Broken Tank
Hello, I was wondering if you can help me. I've rescued a 4ft fish tank and I want to put fish in it, but I have noticed a long deep crack on the  outside bottom. Is it useable? The inside has no crack at least to my eye. Is it worth putting silicon on the cracks? Thanks for your time. Mark Low
<You could try and seal it up or silicone a piece of glass over the cracked area. If it were me I would get a new tank or turn this one into a terrarium for lizards or snakes.-Chuck>

Cracked Tank - Don's Take
I bought the old aquarium (150x50x50 cm) today and it has been 4/5 filled with water. The aquarium is standing on Styrofoam on the floor. The crack appeared on the bottom pane and the water flood my floor :( Is the problem happened because I used Styrofoam for the base? How to fix it? Replaced the bottom sheet is the last thing, I hope.
<Sorry, you need a new tank. The tank must sit very flush on it's stand or the weight of the water can crack the glass. I would not try to repair it. Don>

Ye Olde Aquariume - Marina's Take
>I bought the old aquarium (150x50x50 cm) today and it has been 4/5 filled with water. The aquarium is standing on Styrofoam on the floor. The crack appeared on the bottom pane and the water flood my floor :( Is the problem happened because I used Styrofoam for the base? How to fix it? Replaced the bottom sheet is the last thing, I hope.
>>Yes, it very well may have cracked due to using Styrofoam as a base. 
The bottom pane can indeed be repaired, but it depends on a few things. First, if the crack goes all the way to any edge (where it meets silicone), the entire pane will need to be replaced. Know that all old silicone must be removed, and I mean every last bit. Know that new silicone will NOT stick to old silicone. Know that how the silicone bead is run is VERY important - NO BUBBLES, no corruption of the bead whatsoever, or you WILL have leaks.
Now, if the crack does NOT enter any edge, then you can make a "sandwich" of two panes of glass. You MUST make sure that the entire crack is surrounded by silicone, and you must make sure that no part of the glass is not flush, and does not extend beyond the tank molding, as this will simply cause more cracking. If you're willing to go to all this trouble, then you may have a perfectly sound, if not cosmetically good/pleasing tank. However, it seems to me (maybe due to my aging) that it would be a far simpler and less frustrating process to simply get a new tank. Marina 

Glass Type 
I have a 4' long 18" wide, 18" tall tank. The bottom glass was constructed in two pieces for some reason. Then the seam in the center was covered with a small piece of the same glass, about 4in by 18". It cracked and I need to replace it. 1st, what type of glass do I use to replace this? Couldn't it be replaced with one solid piece instead of two?
Why would it be two in the first place? My thought is that they just used pieces they had available and there it no real reason to do in in two sections.
<I agree... should be one piece... can be quarter inch (triple strength designated some places) "float" glass... Take care in cutting out the old... Bob Fenner> 

Glass aquarium scratches/stability 3/11/05
Thanks again for responding, fast, to my emails earlier this week. I have another question. I have noticed quite a few scratches on the front, and bottom panels to the aquarium. They do not seem to be too deep and my question is can a scratch or a number of scratches cause the aquarium glass to crack over time?
<not at all.. the light scratches are harmless>
I know that the glass panels are 1/2" thick, but can many scratches effect how the glass holds back the pressure from a 150 gallons of water. Let me know, thanks.
<truly harmless... no worries :) Anthony> 

Aquarium Glass Scratch Removal Idea/Experiment
Good Morning,
<Morrow to you>
I’ve searched the archives and was unsuccessful in finding a similar post. Internal scratches on glass aquariums seem to be an accepted annoyance, one I hope to change.
<Great>
As an old fiber optic technician I have several grades of optic lapping film (See http://www.psidragon.com/store/enter.html  for an example) left over from polishing fiber optic connectors in the “good ole days”. I use these successfully to remove scratches from my wristwatch crystals, hence the origins of this Email…
<Okay>
I want to conduct an experiment utilizing said lapping film in an attempt to remove scratches on the inside of my tank and thought it would be fun to have you “involved” via before, during and after photos which I’ll send as close to real time as possible. Sound interesting? If so, we can arrange a date and time that accommodates both our schedules.
<Okay... or perhaps simpler digital/digitized pix over the Net>
The only concern (possibly moot) that I have is that I’m not quite sure what the film I have is comprised of. I’m not overly concerned about the abrasive mineral itself but the glue holding it to the film backing. Any suggestions on testing the film?
<Simple bio-assay... but I would not remove the scratches with livestock, water present... but rinse all out once the removal job was done>
I was thinking of soaking it in saltwater and testing for phosphate, pH etc. to see if any changes occur.
<Could>
Hopefully this experiment will result in something a great many of us can benefit from.
Tim
DuBois, PA
<Thank you for your efforts... reporting. Bob Fenner> 

Aquarium repair
I just picked up a used 150 gallon All Glass Aquarium. The tank is an older model aquarium, and has no center support braces.
<I would likely add a good sized one... either in the middle... half inch glass... or "Euro-style" ones, spanning the inside front and back panels...>
Fortunately, I have a couple of new All- Glass top molding frames, with dual center braces, left over from a 125 gallon aquarium rebuild project that was never finished.
<Oh!>
However, unlike the 125 gallon project, removing the old frame has been very difficult and I don't want to damage the glass. Would you know of or have any ideas on how the remove this old four piece top molding frame?
<Mmm, "it's a bear" no matter which way it's done... all siliconed on... no "magic" solvent... but the use of sturdy bladed hand tools (there are some stout ones for glass install and vinyl flooring industries... sold at Lowe's, Home Depot... to "whack" the frame off in bits/pieces... by thrusting upward... with the blade flush to the glass... a lot of work, but the only way I know how>
Would changing the top molding frame be enough or should I replace both the top and bottom molding frames?
<For function, only the top... or go with the aforementioned bracing ideas. These are further detailed on WWM>
The main reason why I want the change the top molding frame is so I can make use of an All Glass canopy which will not fit properly without the new top molding frame and a canopy definitely wouldn't fit if the tank was to bow out because of the old top molding frame. Let me now, thanks. 
<Ahh, So we are back to the removal/replacement plan... Take your time... can be done... with patience, muscle, tool. Bob Fenner> 

Re: All- Glass tank repair
Thanks for responding back fast. I was determined to get the frame off yesterday and after a couple hours of work I was able to get the old All- Glass top frame off. The only thing I noticed is that the tanks side panels are a little less than 1/2" thick, unlike the front and rear panels that are 1/2" thick. The new All Glass, dual center brace, frame fit nearly perfect (with exception to the slightly thinner side panels), there is absolutely new play front to back or side to side. 
<Good>
So today I installed the new top frame and I also resiliconed all the inside edges to the tank. Some time within the next two days I will test the tank for leaks and if all goes well maybe by the end of the week I can put my 2 Tiger Oscars, 1 Butikoferi, 3 Plecos, 1 Lima shovel nose, and last but least one 24" and still growing Tiger shovelnose, into the tank. Their new tank will be right next to their old tank. Would you recommend using any of their old water in the new tank to help it cycle better?
<Yes... as much of this as practical>
Also, do you think using Marineland Bio-Spira would be helpful in getting the tank to cycle faster?
<Mmm, yes, but likely not necessary... I would move a bunch of the "muck" in the current substrate (gravel-vacuumed) as well>
I do have a slight disadvantage in filtration. The tank came with a forty gallon sump, which I have no space for, so I'll be using three Emperor 400s to filter the tank instead. Would you recommend using anything else to keep this tank clear? Let me know, thanks again.
<The more... the merrier... I would add a big honking canister filter here as well... Bob Fenner>

Repairing cracked 35 gallon tank
Dear Bob, I found a 35 gallon hexagon tank and it has a horizontal crack from left to right on one sheet of glass about six inches from the base. I filled it half way with water outside before it started to leak very little. I have experience and access to cutting Plexiglas sheets, could I reinforce the wall on the inside with Plexi? 
<You could... worth trying>
Would that take the water load and with proper amounts of 100% silicone seal the pressure based leak on the glass? So in essence have Plexi taking the load nearly flush to the glass and the glass acting as the water barrier? Thanks for your time!
<I would give this a go... but definitely "try out" filling outdoors... and not standing near the cracked/repaired panel... Do cut, silicone in "squiggles and all around the edge, pressurize the area to squeeze the Silastic. Bob Fenner>

Glass Tank Repair - James for Bob...
Dear Bob,
<James for Bob> 
I found a 35 gallon hexagon tank and it has a horizontal crack from left to right on one sheet of glass about six inches from the base. I filled it half way with water outside before it started to leak very little. I have experience and access to cutting Plexiglas sheets, could I reinforce the wall on the inside with Plexi? Would that take the water load and with proper amounts of 100% silicone seal the pressure based leak on the glass? So in essence have plexi taking the load nearly flush to the glass and the glass acting as the water barrier? Thanks for your time! 
<Please read the posted link. http://www.wetwebmedia.com/aqrepair.htm. James (Salty Dog)>

Pink silicone
Hi WWM crew,
I've searched Google, my chemistry textbooks, and your website, but I'm not really getting any answers that help me. I have a new-ish tank [about 4 weeks old - 88litres], that is home to three [older] goldfish. Today, when changing the water, I noticed some of the silicone seams were pink. Most noticeably the brace [is that what it's called?] across the top of the back 'wall', on close inspection three of the corner seams are also pink, but not to such a great extent. The brace at the front of the tank is unaffected.  Also, when rinsing the filter [Fluval 2 plus - is as old as the tank] the sponge was an off-red colour. A polyester pad was also in the filter, this was not discoloured. The water is clear. This may be normal, but noticing the pink seams at the same time makes me wonder if they are related?  Due to the tank cycling and huge amount of waste from the fish, I've been changing the water at least weekly, and have never noticed the discolouration before.  I am aware that some products have a pink colour in their sealants, but it is not consistent all along the seam, and has only just appeared.  The fish are not showing any signs of discomfort/illness. All that has been added to the tank is Tetra AquaSafe, Sera Aqutan and Nutrafin Cycle. I feed the fish goldfish flakes once a day, substituted with peas 3 times a week.  I have two older tanks [treated in the exact same way], and have never experienced this - I can't help feeling that something must be reacting [a transition metal?] with the silicone to turn it pink, rather than it being a natural colour change.  Is this something I should be concerned about? Thanks a lot in advance - and keep up the fantastic work!  Kay
< Medications and chemicals can be absorbed by the silicon sealant and give it an off color. Foods with a red base and tannins from driftwood may also leach into the water and eventually discolor the silicon too. But what I think you are observing is a reaction to the lighting you are using. The area with the most pink seems to be the area nearest the light bulb so I am going to take a shot that the silicon is having a photo sensitive reaction to the particular light bulb you are using. I don't think it will affect the silicon but I would still routinely check it for elasticity.-Chuck>

Re: Pink silicone
Hi,
Thanks for the reply. I don't think it is light discolouring the silicone - there is no light bulb in the hood, and the back is next to a wall [so where the pink is, is probably one of the darkest areas in the tank]. The flakes I use do have a red colouring, but this is a fluorescent kind of pink - like someone's run a highlighter along the silicone. Also, there has never been driftwood in the tank, and all ornaments in it have previously been in one of my other tanks with no problems. I'll keep an eye on the integrity of the seams, but I think I can cope for now as it doesn't seem to be affecting the fish. May be worth contacting the manufacturer?
Thanks, Kay
<With the info you provided , I now think it is from the food. Many color enhancing foods have ingredients that may have an ability to stain things. A diluted solution in the water may also stain the silicon over time. I would recommend changing food for awhile and see if the coloration goes away or at doesn't become worse.-Chuck> 

Toluene, rubbing alcohol and resealing tanks
Hello Mr. Fenner,
    I am in the process of resealing a leak in one tank and tearing down one other that has a broken panel.  I searched your FAQs on tank repair and found lots of information, but I want to make sure to get all of the silicone out from between the panels on the broken tank.  I saw that you mentioned using toluene to get the last of the silicone off.  Can this be poured into the seams after most of the silicone has been cut away so that the silicone in-between the panels will come lose or should I try getting the razor blade edge in-between the panels?
<Mmm, not likely. I have used this and other solvents in actually rubbing the glass panels once they are disassembled... and most of the old Silastic removed via single edged razor blades. I don't think much toluene would get into the between glass area if just poured in>
I plan on using the unbroken panels to build a different tank for coral prop.
Thanks,
Daniel
<... Two comments... If you want the cleaner appearing job, you'll want to take the whole aquarium apart and re-do all seams... BUT, maybe you can just adhere a new panel to the outside and inside if you are not going to look much at the tank itself... Bob Fenner>

Inner Silicone seal coming loose
Hi gang,
<Nate>
I'm in the process of cleaning up a 155 gallon bowfront that I bought from the president of the local saltwater aquarium club. It's an awesome tank, and should be much more fun than the current 75 gallon!
<Yes... at least twice as much!>
As I've been working on cleaning things up and getting ready to install a coast-to-coast overflow, 
<?>
I've noticed that some areas of the inner seal are pulling loose at the edges. Nothing is completely loose anywhere, and the tank didn't leak a drop (it's only 3 years old...he's moved up to a 240 gallon now) when it was set up at his place. My question is, should I take the opportunity to re-do this inner seal (I've read all 3 pages of the FAQ on this...and know that
all that inner liner has to come out...not just where it's pulling loose) now, or is it better to take the approach of "If it ain't broke, don't fix it," on this...since it isn't the main seal material that's between the glass? I've never dealt with glass tanks, always had acrylic until now...so any advice will be much appreciated! Thanks, Nate
<This is a tough call... well, let's state the important facts... The only real seal is the bit of silicone between the glass... not the bit above, in the joint/corner... this material is most useful for preventing the jamming of a sharp object (most likely a razor bladed algae scraper) into the actual functional seal/gap... If it were me, mine, I would place the tank on a flat/level/planar surface (on a stand outside that has been shimmed, a good level placed on at all points) and fill the tank... leave it for a day or so... if it doesn't leak, I would NOT fool with it... too likely that the process of cutting away the existing corner material will result in an even less sturdy construct. Bob Fenner>

Re: inner Silicone seal coming loose
Thanks for the reply Bob!
<Welcome Nate>
When I mentioned cleaning up, you responded with a question mark. As mentioned, we bought this from a friend of ours that's moved up in size. I am working on cleaning all the glass surfaces (removing coralline algae build-up and such...general cleaning is all).
<Ahh, good... I took this as cleaning up... as in cutting out the existing seal>
We will indeed be setting the tank up before moving it inside. 
<Good>
I'm re-plumbing it, and will need to check the plumbing for leaks, as well as the tank. I was also there when it was drained, and know how it was moved (with me breaking my back on one end of it to get it into the moving van).
<Yikes... been there>
There was absolutely no leaks in the tank at that time, and it was handled delicately in the moving process.
<Good to check again though...>
From your response, sounds like I'll be best to leave things alone.  We don't use an razor bladed algae scraper, I've got a hammerhead magnetic tank cleaner, and for the harder to get stuff, I use a plastic hand scraper (as did the previous owner...so I'm guessing the inner seal is pulling loose from having the magnetic cleaner catching the edges is all).
<Maybe>
You are a great resource for the aspiring hobbyist! Keep up the great work! Nate
<Will endeavor to do so my friend. Bob Fenner>

Marine tank leaking 5+ gallons a day, brackish algae problem
Hi all at Wetweb.
<Craig>
I am not going to beat around the bush I have a major problem. My marine tank started leaking 2 days ago. I am up to 5+ gallons a day.
<Yikes... where from? That is, have you been able to identify the specific region of the actual leak?>
So I set up my spare 55 gallon tank as a marine tank yesterday. I have the temp up to about 78 degrees right now, and salinity matches my other tank. My problem is I have to transfer all 3 of my fish, about 10 crabs, and a whole lot of live rock 50+ lbs, with tons of life on them including some stony coral that just sprouted on the rock over time (I have absolutely no idea what kind they are, two are green and one is cream really pretty). I have to transfer this stuff all today as the mess from the other tank is just too much to live with. In other words no cycle in the new tank. Am I going to have a massive die off, most assuredly the tank they are in now will give out and all will die for sure, if I do nothing. 
<Should work out fine... do vacuum, let settle the water itself in moving... decanter the solids (throw them away)... and carefully re-stack all... upside up!>
What things do I need to do to help the emergency tank change. I am sure you guys have personally experienced tanks that start to leak to the point where they are unusable, any pointers to help me ease the major upheaval in my marine aquarium's life would be greatly appreciated. Also my sand at the bottom of the tank is very full of life I want to use this in addition to the new substrate but I am not sure what to do here. The old sand is more than likely full of phosphates and other icky nasty stuff. How do I clean this without killing everything in the sand or totally polluting my new tank?
<Please read here: http://www.wetwebmedia.com/movingaq.htm  and the Related FAQs (linked, in blue, above)>
By the time you answer this I will probably have made my decision on what to do, as I am doing this today. But how to take care of the substrate for future reference will be nice to know. As this 55 gallon is a bit smaller than the 80 gallon tank I am moving it from, so a new tank move will be in the future.
Now to question number two.  I have a 120 gallon BW tank with a snowflake eel about 20 inches long now, a dragon fish 16-17 inches long, a lot of sail fin mollies (they are proliferate baby makers too), a gourami (odd he is in there and thriving.  Why is he doing so well? I thought he was a freshwater fish only...
<Mmm, can tolerate considerable salt>
...he is a blue common gourami, and he has been in there 3 years now). Anyway my eel eats ghost shrimp and guppies. I have a guppy problem there are millions of them now, this is recent too, and they always seemed to stay about the same in population, way to many for my eel, and gourami to eat. Although they eat a lot of them. I would like to know what BW fish I can put in the tank to cull the guppy population. Salinity is 1.011. I was thinking 3 or 4 figure 8 puffers.
<Better to simply net them out... the puffers will/would likely keep nipping...>
Next one: I have an algae problem too in my 120 gallon tank, never been a problem before. I read on the internet that I could put a Plecostomus (sp) in a BW system. Seems to good to be true. So I was wondering what I could put in the tank that would eat the algae off the rocks and tank glass. 
<You might be able to acclimate (over a period of weeks) a Loricariid species to 1.005 spg or so>
Ok I realize there must be a source of phosphate causing this so I upped my weekly water changes from 15 to 30 gallons and it is not helping. 30 gallons a week is a major job and I do not want to have to keep doing that.  Also I changed how long my lights are on. Thanks in advance for your help.
Craig
<There are other means of algae control. See WWM re. Bob Fenner>

Re: Marine tank leaking 5+ gallons a day
Hi again I did the change and I found the leak in the 80 gallon tank. I was in the right back corner of the tank under the substrate. It was actually cracked. On the bottom glass panel.
<Yikes!>
The tank is now being relegated to the garbage.
<Mmm, might be able to be salvaged... as a paludarium... or patched and partly filled for... turtles, amphibious plants...? I would list it and sell it>
The change went well all things considered, but now I have one more question regarding care of stony corals in a newly set up tank. What kind of husbandry am I going to need to do to keep them alive?
<Same as you've been>
I understand a new tank is hard on stony corals. The tank they came from was set up for about 3 years and really well established. I am using my metal halides with the 55 gallon and other than that I know nothing about corals, as I never intended on having any in the first place. Just a FOWLR tank, as a matter of fact I did nothing to promote them after they started growing. They just do their thing. I leave them alone and they do fine. Now I moved them... So as you can surmise I have none of the equipment to check for proper conditions for coral. All I have is a hydrometer, and a test strip kit for nitrates, nitrite, and ammonia. P.S. I also found a small yellow starfish about the size of a 50 cent piece must have been a hitchhiker and a green crab also about the size of a 50 cent piece, but it has huge claws, it scared me because the thing jumped out of a live rock piece onto my arm, I dropped the rock lol. I think I scared it more than it scared me. I also found several Bristle worms, one about 12 inches which I removed. I kept the small ones. They eat detritus as I understand it, not living stuff. But the strangest thing I found was a little crawdad thing, really bright red about 1 inch long. None of these things I found were consciously put in my tank, but I think it is wonderful how life can survive being taken from the ocean to the distributor, to the pet store to my house. Put into my little slice of the ocean and thrive, then surprise me years later by being seen for the first time. Makes me wonder what else is in the tank, that I still have never seen. Just simply amazing to me.
Craig
<What a planet eh? Please read here: http://www.wetwebmedia.com/marine/inverts/index.htm  re: stinging-celled life care.  Bob Fenner>

Tank bracing
Hi guys-
<Steven>
I am getting ready to move my glass tank (5x2x2 with 10mm glass thickness) and thought that this would be a great opportunity to possibly do something about the 12" center brace that is causing a bit of headache with my lighting. From the other posts that I've read that have had bowing issues, this is exactly the type of bracing that you have recommended to resolve their problem. However, I wanted to ask if it is possible (safe) to remove the center brace and replace with two braces that are not as wide (approximately 4-5") that will divide the top of the tank into thirds so that I can place my three MH in between each of them? I have looked on www.garf.org DIY tank building pages, and the only bracing that they recommend was a 2" brace (10mm thick) running the perimeter of the tank. I was thinking of doing this as well as the proposed two other interior braces to try and be as safe as possible. Does this sound plan sound alright to you???  Thank you so much for your help.  Steve 
<This so-called European style bracing is useful... I have it with my Eheim units... But I would increase the width of the material to three inches, and if you had more than 10 mm thick glass (12 or even wider), I would use this for the strips... 100% silicone them inside, about an inch down from the top. Bob Fenner>

Cracked fish tank?... doomed?...
Hey Bob,
First.. thanks for having this site.. it's always been a great help for me.  I have read through the FAQ about tank repair, but can't quite seem to find one that's my situation.  I am about to get a deal on a 100 gal tank (for 100 bucks, maybe less), but the problem is there is a crack in one of the corners and the seller told me that a small amount of water leaks from the corner.  I was wondering (before I buy the tank) what would be the best way to fix it?   Re-seal that corner?
<Risky, but could work...>
Or am I just wasting my money buying this tank?  The crack is about half way up ( here is a pic.. it's blurry cause she doesn't know how to take close up pics).  Any help would be GREATLY appreciated.  Kevin
<If it were me, I would NOT buy this tank if you intended to fill it all the way to the top... VERY likely it is fine being partly filled... a nice turtle tank... paludarium... or? Bob Fenner> 

A crack in 180 g aquarium
Hi!
<Hello... don't know if this was responded to already...>
I read your web site almost daily.
<Me too>
My husband and I had a dream to have a reef aquarium built into a wall. He bought the half inch glass panels and siliconed them together and used straps to hold them together while they dried. the measurements are 59"X22"X32" (LXWXH).
<Wow, a high aspect>
it works out to approx. 180 g. We built a wall around the aquarium. this all took place about 2 years ago. we saved all our pennies to start this $$$ project.  we finally could afford it and had a professional come over and set us up. He did all the plumbing and we filled the aquarium with water to test the aquarium, pumps, sump etc. about 6 hours later, the back panel cracked from top to bottom.
<Yikes>
we had water everywhere! the aquarium was not reinforced with braces) Thank Goodness the only thing in the aquarium was tap water!!
<And no one was hurt... Very dangerous>
I have now done a lot of reading mainly on your site and would like your advice.  We were hoping just to replace the panel. Should we take the entire aquarium apart and clean and resilicone the entire thing or just where the new panel will go?
<Just the last>
How do we hold the newly siliconed aquarium together for drying since we no longer can run straps around it because of the walls we built?
<Wide tape will likely do here, or if you have wood clamps... you might want to borrow from a woodworking enthusiast friend... or go see these at a large hardware store... can be "top-mounted">
How many  braces should we use and how thick?
<Mmm, very important to relate this adequately... please read, re-read this a few times: EITHER (what I would do), a four inch wide strip siliconed inside the front AND back pieces about two inches down... of length all the way to the sides, and/or  a one foot wide piece in about the middle, set down inside the front and back about level with the top edge>
it now stands on a steel frame that my husband welded together. it sits on top of plywood and Styrofoam. Do you think the stand could have 'given' and caused the crack?  
<Yes, possible. And once again, VERY dangerous if it did, can>
Please help us because my husband is ready to turn it into a terrarium but I want my little piece of the ocean.  I have had freshwater fish most of my life and now I am ready for this adventure.
Thanks so much.
Liz
<Bob Fenner, who thinks this size, shape would make a delightful paludarium as well...>

Emergency move!  30-gal Tank got a leak
Dear WWM crew:
<Paul>
I never start an email to you guys without thanking you for everything you do... So thanks!
<Welcome>
It seems I am running into bad luck after bad luck starting up my aquarium.  I converted my 30-gal FW to SW and got a 10-gal as a QT tank.  My fish (two clowns, one Gramma, 5 hermits) seemed happy, ate relatively well, and were moderately active.  The Gramma mostly came out of the live rock for feeding, after which he would promptly go hide again.
<Typical. Give it time>
I woke up one morning to find a huge puddle on the floor and a good portion of the aquarium's water level gone!  The aquarium was leaking, so I decided to put everything in my 10-gal.  I filled the bottom with sand, put as much live rock as I could without stacking it while still making caves, filled it with water, and got my fish to safety.  Now, here's where my confusion comes in.
My fish are much more active!  At feeding time, they are extremely anxious to get food, and will even take it out of my hand if I do not let it go in time!  The Gramma no longer spends his time hiding within the live rock.  The crabs are much faster than before.  Is this a bad thing?  Should I take this to mean the fish are happier, or just frantically claustrophobic?
<Something/s are different... maybe you've raised the temperature... perhaps just a good water change...>
I know small aquariums are dangerous because it's harder to keep the water quality consistent.  However, if I have the water tested by a LFS weekly, would it be impossible, and would the fish be unhappy?  
<No store, no agency is able to actually test for all...>
Since I live in a small apartment, the small aquarium looks much better than the large one, the fish are more active, eat better... everything seems to be better, except the actual size of the aquarium.
I have been maintaining this small 10-gal mini-reef like this for the past two months.  I've been changing 25% of the water weekly, and the water I've been taking out of the aquarium, I've been getting tested the same day.  If I am diligent about these parameters, is it possible I may keep the aquarium as is?  Or is it still ridiculously small?
<Mmm, you may have good success for a good long while... much of the probable negative interaction twixt and between the clowns and Gramma has been eliminated through their introduction in the larger tank>
I only ask because my 30-gal is useless, I can't afford a new tank at the moment, and I'd have to give the LFS back all my fish and live rock... and something close to a $500 investment will have been wasted.
Thanks for your time!
Paul Ghica
<Paul... did you actually ever find the leak in the thirty? Very often such "leaks" turn out to be gear failures, splash and spray from a powerhead, diffuser... I would definitely set this tank up (outside) with newspaper under it, and CAREFULLY fill it, check for the actual source (if any)... and even IF it did leak, I would simply reseal (silicone) the inside corners... easy to do. At the very least, sell all to someone who will test, repair it. Bob Fenner>

50 gallon aquarium crack
Hey guys,
I just upgraded my 50 gallon aquarium to a 90 gallon. I noticed after setting the 50 up again, with no water in it, that there was a 3 inch crack starting from the bottom back right corner and extending towards the center of the bottom pane. The crack isn't all the way through the glass, just on the inside of the tank. I was really looking forward to using this tank to breed convicts, but now I'm worried to fill it with water. Can I just use 100% silicone to cover the crack? I really have no idea how to repair something like this, any advice you could give me would be very appreciated. Thank you for all your help.
You guys are great!
< To be 100% safe I would replace the tank. Especially if it was in an area where water would be a problem on the floor. You can try to repair it by cutting a piece of glass a little bigger than the crack and siliconing it in over the crack. I know this works on the sides of the tanks but have never had to try it on the bottom.-Chuck>
Todd Munger

Aquarium Disaster Prevention - and a small bubble in the glass
Dear Sir / Madam,
Upfront - My question is  - how do I detect if an aquarium could crack or burst. Are there any notable things to look for?
Here are my details leading to this question (my apologies for lengthiness).
- Last night (new years eve) I heard a "slight bang" come from my 65 gallon aquarium (long).
After inspection everything seems ok. Except for a small crack in the plastic molding at front top
right corner. The molding is siliconed to the glass but the contact area of the silicon is about 1/2" up - away from the crack.
That crack may have been there all along - or it may be new. Yesterday I had worked on the aquarium,
replacing 1/2 tank of water as I do almost weekly.
Also - there's a small bubble inside the front glass pane I didn't notice before - its 1/2 way up and near the same side of the tank as the molding crack. Its about 1pinheads wide, crest shaped.
- The tank (Miracles Aquariums brand ) was bought with a pine stand - all sides are supported under the tank. We bought it new in late August. Its a freshwater, fully planted, lots of fish, co2 injection, some wood ,rocks and about 2 inches natural gravel across the bottom. The lighting canopy never did properly fit over the sides. the top molding does have a bar through its centre. I'm thinking the whole system is max 1200 lbs.
It sits in the living room corner -along a retaining wall in our 50 year old apartment, but not across the joists. We felt that it was better to have it along the retaining wall than across the joists in the center of the apartment - in our limited space.
- We've placed a piece of wood (pine) about 1/4" high and 3" back - as a shim underneath the front of the stand,
as we had noticed the floor slightly drops towards the centre of the room.
The floor also drops from left to right about 1/4" across the aquarium.
I'm thinking that slight shifting over a few months time could crack the molding at a pressure build up point.
But wouldn't the glass have cracked? Or can glass ever so slightly curve?
Could a bubble in the glass mean trouble?
Thank You in advance for your time and efforts.
Any help with this source of insomnia is be greatly appreciated.
< You have two things to be concerned about. One is cracks and the second is leaks. Planted tanks and reef tanks have pretty high lighting requirements. These high intensity lights generate lots of heat. As the lights are turned off and on the plastic molding expands and contracts accordingly. The plastic loses some of its elasticity over time and may not totally rebound and develop a crack. These cracks may develop leaks through condensation under the lip and should be resealed. Cracks at the top of the tank usually are not structural. The top of the tank has no pressure put on the joints. At the base of the tank a setting floor could case uneven settlement and put stress on one point of glass over another. That would case a crack and a leak. Bubbles are a structural weakness in the glass. I would recommend a better safe than sorry approach and check the tank and floor to see if they are level. If not then you may have to consult a structural engineer to see if you floor are capable of handling this long term strain on your floor joists.-Chuck>
R Ryan

Algae in scratches on glass
Hello;
<Good evening>
I have scratches on the inside of the glass of my 55 gal reef tank.  I'm not sure whether I created these scratches by using a metal scraper blade to remove coralline algae, or by using an algae magnet (I hear both actions, if done improperly, can scratch the glass).
<Yes>
Green algae grows in these scratches easily, making the scratches quite visible ;-) and making the tank generally ugly.
Assuming there's no easy way to actually remove the scratches, what's the best way of removing the algae from them?  None of the algae removal items (pads etc.) I've bought from my LFS seem to work.
Thanks!
<Other than techniques to make nutrients scarce through chemical filtration and/or competition, there is little you can do here. Are both sides of the tank scratched? One side may be better to turn as the front... The above methods are detailed in various places on WetWebMedia.com under marine algae control.
Bob Fenner>

Silicone
Can you tell me which brand of GE Silicone is reef safe? Silicone I, II  window or kitchen and bath?
Thanks
< Use only the silicon that specifically says on the package for aquarium use!!!! All the others have midewcides that will kill fish.-Chuck>
<<ed. note: GE Silicone I has been aquarium safe to date, but II is not.>><<<Common progenitor's note: 100% Silicone will do it... RMF>>>

Aquarists worst nightmare...
So I woke up at 2:30 am last night to every aquarists worst nightmare.. the sound of gushing water.... The front pane of my 40 gal. reef  split from top right side all the way down to the bottom. Grabbing all the Rubbermaid containers, and buckets I could I ran out there and tried to catch as much as possible.. I think I saved about 15 gallons, while the remaining 15 or so marinated the wood floor.
Some good news though. Ran out to the store first thing this morning got a new 30 gal tank, I think all corals, fish, crabs, and snails survived, and are now living happily in a (slightly cloudy) but new tank with a brand new 6 inch sand bed. (I was lucky enough to have 90 lbs of  aragonite still out in the garage..)
I tried to save as many sandbed clams as I could from the old tank, but only found about a dozen.. ( I couldn't find about 6) not to mention all other life such as worms, copepods, and other misc. bugs that were flourishing in the old sand.. (I couldn't put the sand it in the new tank, b/c of the toxic sulfur dioxide that I could smell after stirring it up looking for my clams.)
lessons learned:
* Can never have enough buckets, and towels around in this hobby....
* Always have spare heaters and powerheads...
* Lastly, (and by far the coolest) Cerith snails are the hardiest things on the face of the earth... I took the tank outside last night after draining it, so it wouldn't spill any more muddy muck all over my floor.. I went out this morning, ands on top of the sand were 5 dried up Cerith snails that had been outside, out of water, in 38 degree temps for 8 hours. I thought what the heck and threw them in the refugium, and within 5 minutes they crawled up on the glass. Who'd a thunk?
Any who, my zoanthid fragging will be somewhat delayed due to these unforeseen circumstances. Just wanted to share my story with my fellow reefers. Ciao.
J. Blair Miller
<Thank you much for sharing... What an ordeal! Glad to see your intelligence, balance has survived along with most of your livestock. Any idea what caused the tank to split? Bob Fenner>

To brace or not to brace, actually to use or not to use
Hi Bob
<Chris>
Thought I'd do this as a reply to your last email, rather than a new email, so you can see the texts of our previous exchanges.
<Okay>
Well, as of this evening, tank construction has finally begun. But problems have emerged, and I would really value your advice.
I have used this glass supplier for a number of projects, but never for aquarium glass. I've always found their cutting accurate, and therefore this time I just quickly checked for overall dimensions, not for right angles on faces or edges.
MISTAKE!
A number of the glass edges are not at right angles to the face, and two of the sheets - a side and a front - are not perfectly rectangular. This means that the front glass - the final piece, and therefore the one where the mistakes accumulated - has masses of air bubbles in the silicon seal which I could not eliminate - even when banging pretty hard with a rubber hammer.
<... not good>
Where some of these bubbles reach the outside of the seam - inside and/or outside the tank - I intend to run more silicon into the gaps tomorrow. But numerous bubbles will undoubtedly remain. How disastrous is this? And if you think it is disastrous, what can I do about it?
<Can be real trouble... the only real strength in these constructs is the silicone between the glass to glass surface area... less of this area, or more gap between the sheets, bubbles... equals less strength.
And just for future reference, was I wrong to keep my bead of silicon to 1/4 inch for 1/2 inch glass? Should my bead of silicon have been of the same thickness as the glass (1/2 inch)?
<Mmm, nope to all... as stated, the real strength of these joints is just a smear of silicone... the rest of the material is to protect, more or less, cutting into this area (between the glass sheets). Some tank manufacturers in Europe like Juwel, actually leave off any "extra" silicone... and folks who know how to use silicone really well, can make a whole bunch of tanks whereas sloppy folks (like myself) don't get near as much per volume of silicone>
At the back left of the tank, where the side piece of glass is not perfectly rectangular, the gap at the bottom is 3 mm (1/8 inch), but that can be filled with silicon. Again, how disastrous is that?
<Can be tremendous... I encourage you to make the current tank into a terrarium... or a snake et al. enclosure... really... and start over with panels that will leave NO gaps>
And just to end my tale of woe, the left side piece is 4 Mmm (3/16 inch) above the top edge of the back glass, and the right side piece is 3mm above the top edge of the back glass. Which means that if I run my bracing strip along the top edge of the glass (as we discussed earlier), there would be a 3-4 mm silicon-filled gap between the bracing strip and the top edge of the back glass. Any thoughts on this?
<This is not so much of a big deal... and some more bracing can be cut, fit, siliconed to fit inside and attached to this "on top" bracing if so desired. HOWEVER, I would NOT use this tank with the gaps stated as a water-filled container. Sorry to be the bearer of bad news. Bob Fenner>
Thanks in advance for your help,
Chris

Commercial Aquarium leak in Ireland
Heh, sorry to send a private message but couldn't find anything on the forums; I think it may be because I need info about a commercial tank and most posts are about private glass tanks.
<No worries. Welcome>
I am a member of staff in a 35 tank native marine aquarium on the west coast of Ireland.  The supervisor recently resigned and left me (completely inexperienced, I was a chef in a previous life) with the task of managing said aquarium. Anyway, I have a large 8 cubic metre tank
<Now, that's a tank!>
that houses conger eels.
<Neat animals... around the world these largish eels can be approached (even handled) with impunity>
  This tank is made of what appears to be concrete with a 2 metre square Acrylic window set about 1 metre off the floor.  A very slow leak has appeared to the right and below the level of the window. I drained the tank and re-siliconed the window panel on all three sides but had a gut feeling the leak had nothing to do with the window.
<Happens>
I could have sworn I saw some kind of suction or movement in the base of the tank when there was a couple of inches left in it.
<Yikes... dangerous>
Now the tank is refilled and conger back in. I think I need to find the location of the leak so I know what I am up against, does anyone know how I might find it?
<This can be a very trying ordeal... as the water can actually originate most anywhere within (or even outside...) the system and appear most anywhere outside... there are some techniques using dyes of differing densities... but I encourage you to go the perhaps expensive route of having a structural engineer firm come in and inspect the system (and all others of size there)... and consider the route of draining, drying, and resurfacing the entire inside (I would remove, clean the race/facing panel, and re-silicone the viewing panel after this) with a water-proof material (likely an epoxy)...>
Some kind of dye? Or is there product I can put into water that will automatically be sucked into the leak? Thanks for any help you can offer
Alex Stewart
Lahinch Seaworld, Ireland
<Oh, see you're aware of the dye... these can be carefully placed in layers (by density) and a spectrophotometer used on the subsequent leak water to detect at which level/depth the water is escaping from... As stated though, I would have the system inspected for structural integrity overall... and re-fit, re-do the entire inside. Bob Fenner>
Lahinchseaworld@eircom.net

Foggy glass
I have a 135 RR Oceanic tank that I purchased used. It was previously used as a cichlid tank. The tank has been sitting in dry storage for almost 2 years. When I went to clean it, I noticed the (inside) front glass panel is foggy. I have tried hot water, vinegar and rubbing alcohol, but once the cleaning fluid dries the fogginess reappears. Is this normal? When I wet the glass it looks perfectly fine? I have never heard of glass getting old.
Would soaking help? Any clues?
< Two things could be going on. The glass could be scratched and there is not much you could do about this. If it is precipitated with  mineral deposits then wipe down the tank with a vinegar and or lemon juice to dissolve the minerals. This is pretty common for a used tank. Be sure to check the silicon for leaks.-Chuck>
Thanks, Ken

Possible tank leak??
I think my tank is leaking and now I am concerned. I am losing up to about 3 gallons a day on a 120g at first I thought it was a evaporation thing. Today while filling up the tank I noticed where the doors join when closed salt creep.
<Mmmm, maybe splash or spray...>
I have checked bulkheads all seem fine. The outer edges where I can see where the tank joins from sides to bottom is free of salt. no salt evidence down the seams.
The plywood the tank is sitting on seems dry.... I really do not want to break everything down again,
Suggestions comments welcome,
Lee
<Try taking some toilet tissue and wiping about at all plumbing fittings, joints, seams of the tank... even a small amount of water should show. Do check about for errant spray, splash as well... this "adds up" over time... may come from a pump discharge, mechanical aerator... Bob Fenner>