Plumbing question, sump   12/13/07
Hello,
<Hello Jeff.>
I hope all is well with the WWM crew!
<It is on my end, trying to spread Christmas cheer.>
I just purchased a used 72 gal bow front. I am trying to get the plumbing worked out and have a few questions. There is a 20 gallon long sump.
I have a quiet one 4000 return pump stepped down to 3/4 inch with a ball valve for my return. It has about 4 ft vertical head with 1 90 degree elbow. I used the reef central calculator and get 587 gph as my return rate. My overflow is just shy of 1 inch id, 9/10" as far as I can tell. The bulk head has a barbed connector for flexible PVC so it robs a tiny bit of diameter.
<OK>
I am trying to figure out how much flow the overflow can handle. I tried dumping water down the overflow and timing the gallons for a minute and I got a flow
rate of 240. 4 gallons in 1 minute = 240 gph. I read somewhere in the FAQ that I should get around 300 gph for a 1 inch overflow. Is this the max?
<Yes, 240 for this set up sounds reasonable.>
I am using a Durso as well.
I had the return pump running full blast for several hours and the tank did not overflow so I can not figure out how the overflow can keep up if it only handles 240 gph out but the return is blasting 587 back in.
<The pump is likely not actually flowing this amount. Calculators tend to be overly optimistic. Is there an intermittent flushing/slurping noise? Overflows can flow more than specified by creating a siphon, but this cannot be trusted.>
I want to add another pump and plumb it up the back of the tank and then T it off to make 3 outflows along the back instead of power heads. I would like to run this pump from the sump as well but I don’t know if the overflow can handle it and I don’t want a mess on the floor.
<The overflow will not handle this.>
Is there some error in my calculations? If not should the tank already be overflowing?
<If you flow the bulkhead at its absolute limit you will likely end up with water on the floor sooner or later. It becomes a balancing act that you will eventually lose.>
Will I be able to add the pump, I am thinking another quite one 4000, to the sump or will I have to draw the water from the display?
<Definitely intake from the display.>
I am trying to get as close to 1400 gph turnover as I can. I am planning this tank as a soft coral with fish display.
I have a 30 gallon FOWLR now but it is not drilled and have no sump. This is my first plumbing project. Thanks for all your help and for your great site. I spend 2 or 3 hours a day reading through it for the past several months steady planning this.
Kind Regards,
Jeff
<Great to hear, keep reading. There is a wealth of knowledge available. Welcome, best wishes, Scott V.>

Question Regarding Two-Pump Sump And Refugium Return Setup – 12/13/07
Hi,
<<Hello>>
I can't seem to find an answer to this question in your website and I'm wondering if you can help me.
<<I shall certainly try>>
I have a 110 gallon FOWLR with a wet/dry sump and an Eheim Hobby 1262 return pump (900gph) that is currently running.
<<Okay>>
I'm planning to add another sump just for refugium (live rocks and macro algae) and use my Mag-Drive (1200gph).
<<Mmm…>>
Would there be any problem if both sumps (with different pump speed) are running separately into the same tank??
<<Even though you have not provided any information re your plumbing scheme (Number/size of drains, how these vessels will be “fed” from the tank), I recommend you do NOT try this… Even if the drains are sized appropriately for the flow rates, you will have great difficulty/an impossible task keeping the flow regulated for the individual pumps (and before you ask…no…valves on the drain lines are not the answer). What is most likely to happen is the flow will equalize between the overflows causing one pump to starve and one pump to not keep up (overflow the vessel). Even if you use dissimilar drain diameters, the smaller will be overwhelmed and surge…with the resultant noise and bubbles. Nor is utilizing two pumps of the same flow/manufacture going to work as differences in head-pressure caused by subtle differences in plumbing, even differences in the rate of buildup of bio-film within the plumbing, will still keep the flow from being exactly the same between the two. Your best option is to plumb the refugium to gravity-drain in to the pump chamber of the sump (fed by one of the drains). And there’s no reason you can’t put both pumps here (the sump) if you wish to have the extra flow…assuming your drains can handle the total output, which for the two pumps you have listed I recommend three – 1/1/2” drains OR two – 2” drains …minimum…>>
Thank you in advance for your response.
Regards, Miguel
<<Happy to share Miguel… Do write back if what I have stated is not clear or you wish to discuss further. EricR>>

Flow through sump, des.  – 10/28/07
Crew,
Thank you in advance.
<Scott V, glad to be here with you.>
I came across something that I had not considered before today and want to run it by you. I'm setting up my 240g with 100g sump. I've done some testing with my return pump and it's giving me about 2400 gph with my current manifold configuration. I have four 1.5" drains along the back wall.
<Nice big tank with big sump. Good safety margin on overflow size vs. flow.>
Seeing how I do not want powerheads or a CL, this 10X turnover is about right for my planned inhabitants. My only concern is that 100% of this will be through my sump. I am not concerned with the noise aspect of this set up as everything, sans display, will be a through wall set up in the garage. Today I read something about in sump skimmer inefficiency with too much flow through the sump. (I have Euro-Reef RS250) Have you heard of this? Should I be concerned? What exactly are they talking about? Have I overlooked any other drawbacks to this volume through the sump? Any advice is appreciated! Thanks,
Ben
<The ideal setup would have just enough water coming through the overflow as the skimmer can process, the overflow would skim a thin layer of surface water and it would flow directly into the skimmer. This will give you the highest concentration of the organics you want your skimmer to remove and theoretically give you the highest efficiency per pass (these same compounds your skimmer removes are the most concentrated on surface). The issue you are reading about is the fact that too much flow will dilute that surface water, thus your skimmer sees less of these organics per gallon, technically being less efficient per pass. The flow through the sump and its effect on the skimmer performance is a matter of optimizing, not necessity. Fact of the matter is you have a lot of carrying capacity with your tank, you add to that a large sump and you picked out a awesome skimmer that will still perform great. Have fun, sounds like a nice setup, Scott V.>

Sump/Overflow Question…Best Way To Temper Flow? – 09/01/07
Good morning all,
<<Greetings Daryl…evening now>>
Thank you again for the world of info on your website.
<<A collaborative effort…we hope you find it useful>>
I hope this finds you well.
<<Doing fine, thank you>>
I recently moved my 55-gallon FOWLR to a 75-gallon aquarium with an overflow. In the 55 I was using a canister filter and skimmer; the 75 is my first venture with a sump.
<<A worthwhile change/upgrade>>
I am currently using my CPR hang-on skimmer with the 75, planning on eventually using a skimmer in the sump instead.
<<Ah good…perhaps one from my current fave, Euro-Reef>>
The sump is a Megaflow 2, which is sized for a 75-gallon aquarium; my return pump is rated at 950 gal/hr. Sump intake is through a 1 1/4" hose and is output through a 3/4" hose connected to the pump (not split). My question is this: The volume of water coming into the sump tends to overflow the prefilter pad daily; I rinse or change the pad, which quiets things down for awhile, but in about 24 hours I am back to overflowing the pad.
<<Perhaps a coarser pad would not clog to quickly>>
The water in the overflow bubble chamber is approximately 3/4" above the prefilter tray, which seems (to me) a bit much.
<<Why, what problem is this causing?>>
What is the best way to lessen the water coming in to the sump?
<<Reduce the volume of water being pumped up to the tank>>
Am I better off installing a valve on the intake to lessen the flow into the sump, or would I be better off splitting the return to the tank?
<<Don’t place a valve on the drain line, but rather, install a “gate-valve” on the “output” side of the pump to temper flow as needed>>
My guess is that splitting the return would be a better option, as I would also increase water movement with a second output, but I would very much appreciate your opinion.
<<You can split the return if you wish…but do still install the valve for best “control” of the flow rate>>
Thank you in advance for all your help.
<<Happy to assist>>
All good wishes,
Daryl
<<And to you in kind. EricR>>

Re: Sump/Overflow Question…Best Way To Temper Flow? – 09/03/07
Sorry to bother again...very quick follow up:
<<Hey Daryl! No bother mate>>
I have a check-valve on the output of my pump.
<<Is a mistake to use/rely on these devices in my opinion. Much better to design/install plumbing such that the sump will handle all transient water volume. The check-valve imparts significant resistance requiring a larger pump (and associated cost/energy consumption) than normal, and will most assuredly fail at some point>>
If I install a gate-valve, should it go inline before or after the check valve? I would assume the gate-valve would come first, followed by the check-valve...
<<This might be fine (If you are determined to keep the check-valve). Though depending on the size/type of valve and how much you need to reduce flow, you may find that the valve stops all flow before the desired rate is reached if the gate-valve is installed first. This is probably of little concern, but a bit of experimentation will tell>>
Thank you again, and all good wishes,
Daryl
<<Happy to help. EricR>>

Some General Questions On Sump/Closed-Loop Plumbing – 07/03/07
Hi.
<<Hello>>
I was wondering if you could please answer a few quick questions regarding plumbing.
<<Sure…ask away!>>
I am setting up a 135-gallon reef with 55-gallon sump.
<<Very nice>>
Currently the tank has 4-holes drilled in the upper back glass panel that fit 1-inch bulkheads.
<<Okay>>
I'm planning on using all 4 as overflows out of the tank.
<<Do figure only about 300gph per…still, 1200gph is a LOT of flow to process through the sump (if that is your plan)>>
I was planning on plumbing 2 of the overflows down into the sump where an Iwaki rxt30
<<I think you mean the 30RLXT?>>
(19 gallons/minute at 0 head) will return the water back into the tank (approximately 5-feet head).
<<Be sure to plumb a “gate-valve” on the output side of the pump to allow tempering of the flow if necessary>>
The other 2 overflows I planned on incorporating into a closed-loop system with another pump similar to the Iwaki with similar flow rate (I don't have it yet).
<<Ah! Excellent…but you really only need one of these throughputs for this purpose>>
Would the two 1-inch overflows per pump be sufficient to minimize sucking and gurgling noise, or should I plumb all 4 overflows down into the sump, forget about the closed-loop and use some powerheads instead?
<<If you keep the flow rate for the sump drains in the range I suggested you will likely be fine, although even then sometimes a bit of tweaking (aspirating the lines, experimenting with different configurations of the termination ends, etc.) can be necessary due to the vagaries of system design. As for the closed-loop, a single throughput directly plumbed will be enough to supply the pump (the fluid dynamics are different than those associated with “gravity” drains). You could use the last bulkhead to supply the sump and be even further ahead of the game…or even use it to supply an in-line refugium>>
Or even a third option: use 3 overflows for the sump and 1 for a closed-loop with a smaller pump?
<<You can do this with you current planned pump. Unless there is something about your design that will restrict the water volume (e.g. – bushing “down” the pipe size), as long as you match the bulkhead/pipe diameter to the intake port on the intended pump you should be fine>>
What size (flow rate) pump would work ok with a 1-inch overflow to minimized gurgling and sucking noise?
<<As explained…unless the throughputs are positioned very close to the surface where a very strong pump/flow rate may create some cavitation. But again, be sure to plumb a gate-valve on the output side of the pump>>
Also, on the return plumbing from the sump (and closed-loop if there will be one) should I reduce the 1-inch return pipe just before it enters the tank after the T, or should the two pipes putting water into the tank remain 1-inch (the output on the pump is 1-inch)?
<<Reducing the diameter as you indicate often makes the return easier to handle/place/disguise, but will also reduce flow/add to head pressure…as will that “T” you mentioned. All the more reason to slightly oversize your pumps and adjust flow with the gate-valve if needed. For the closed-loop, to will need to reduce the terminal ends/nozzles to ½” to achieve a useable velocity…and then likely no more than two of these (for closed-loop applications figure about 350 – 400 gph per ½” nozzle)>>
Lastly, should the bulkheads be slip or thread on the outside of the tank portion?
<<Is up to you>>
I want thread so they can easily be removed just in case, but am worried about leaks.
<<I wrap my threaded fittings with several layers of Teflon tape…or you could smear some silicone sealant on the threads just before assembly and let it cure before use (this doesn’t “glue” the joint but does help greatly with creating a drip-proof seal>>
Your expert opinion would be greatly appreciated here.
<<Mmm, don’t consider myself an expert…but prefer to think of myself as a “student” of the hobby>>
Thank you
Jon
<<A pleasure to assist. EricR>>

Regulating The Flow Through My Sump/Refugium – 03/09/07
Hi,
<<Hello>>
I just have a question regarding the flow rate through my sump/refugium; I’ve done a lot of reading on WWM but can’t find the answer I’m looking for. (sorry if I’ve missed it).
<<No worries...let’s see if I can help>>
I’m just about to start building my sump tank, the first chamber shall house the skimmer, the second will be the fuge and then the return, the whole sump tank is roughly 25 gallons so the fuge shall hold roughly 13 gallons.  The skimmer shall be gravity fed with a “T” junction before the skimmer taking excess water from the overflow (which can handle 2400 litres per hour) into the refugium.
<<Ok...roughly 630 gph, for us colonials [grins]>>
Obviously the water from the skimmer also will flow into the fuge.
<<Yes>>
After a little research I’ve read that the flow through the refugium should be very low, (max 10x the fuge volume).
<<Depends really...a bare bottom refugium with Chaetomorpha macro-algae would likely be fine...but yes...generally, flow rates are 3-10 times the volume of the vessel>>
The way I have first planned (above) means that all the water coming from the overflow would go through the fuge (2400 litres per hour) which I now know is a lot.  The problem I have is that I want to use as much flow as possible to help with turnover but at the same time keep the flow through the fuge down.
<<I suggest you give it a try and see how it goes>>
I did think to bypass the fuge (from the overflow and skimmer) to the return chamber and “T” off the return pipe with a ball-valve and have some water redirected into the fuge but I still have water from my skimmer going into the fuge which will be around 800 litres an hour.
<<And is a mere 210 gph...should do nicely in my opinion>>
Would this be the best way to achieve this or am I missing something?
<<Not “missing” anything, I think this will be fine>>
I hope that all makes sense.
<<It does>>
Thanks.
Leo
<<Quite welcome, EricR>>

Sump Flow Rates and Powerhead Opinions - 2/20/07
Hello.  
<Hey Pam, JustinN with you today.>
I've been combing your Q&A's looking for the answer, but haven't found it yet.  
<Ok>
I'm getting conflicting advice from my LFS who seems very knowledgeable, and also from one of the most highly regarded forums...also seemingly very knowledgeable reef-keepers.
<Often is just a difference of methodology, not necessarily one whom is right or wrong.>
I'm buying a my first tank and have been doing a ton of research (books, online forums, LFS)
<Excellent, this is the starting point of a successful hobbyist for certain.>
I'm buying a 54g corner tank, with a Oceanic Micro Sump (approximately 15g...only thing that will fit in the stand).   
<Sounds good>
My LFS recommends a Eheim 1260 return pump in the sump (flow is 635gph which is about 11 times my display size) plus 1 power-head in the display, and the reefers on the forum, recommend the smaller Eheim 1250 (317gph which is about 5.8 x my display size) with 2 power-heads in the display.  They're saying the 635gph through a 15g sump will be too much flow through the small sump, causing lots of noise and micro-bubbles.
<I would agree with the fellow reefers here, my friend. You could likely come up with a baffling system to negate a deal of the micro bubbles, but chances are you will always be competing with them from that flow, to some extent. Also, there's the factor of having to match your overflow rate to the sump, with the return pump -- at higher flow rates, can be harder to do.>
I know from reading lots of your Q&A's, that you are anti power-heads in the display, but do you think the 635gph will be too much going through a 15g sump?   If it's not too much, will that be adequate flow without any power-head in the display at all?  Your points regarding powerheads definitely make sense.  
Thanks so much!
Pam
<I would not say that we are anti-powerheads here, on the opposite side of the coin, I think that we are for the right solution for each individual tank, to which there is no steadfast rule, or specifics. Powerheads are very effective for their purpose, and can be utilized without great issue here. If you wanted to eliminate the powerheads in your tank though, do consider having another overflow and return plumbed into the tank. You could create a 'closed loop' here, utilizing a pump such as the Eheim 1260 and bypassing any excess filtration methods, just draining water from the tank into the pump system, and returning its flow to the tank itself. Both methods will serve your purpose just fine, my friend. Keep up the research, and welcome to the hobby! -JustinN>

Sump Questions, des.  2/19/07
Hi Crew,
<Hello>
My current setup is a 30 long display tank with 30lbs of live rock, 2 Aquaclear 50 powerheads (turning the water about 18x), sponge filter, so I am ready for quarantine, Prizm skimmer (I know these skimmer aren't the best).
<In my opinion, they are a good skimmer for smaller tanks such as you have.>   
There are no fish in the system yet, just Turbo snails, Nassarius snails, Red Striped Hermits, and tons of copepods.  It is my first saltwater tank and it matured very quickly due to the 100% cured live rock from my LFS.  My only regret is I wish I had bought a larger tank.
<Always best to go with the largest system you can afford.>
I am thinking about adding another 30-gallon long aquarium and converting it into a sump/refugium underneath
<Whoa, if you should lose your siphon, you will pumping more water into the display tank than it can hold.>
to really increase the copepod population and filter nitrates.   
The reason I want my sump/refugium so large is because I will probably be upgrading to a much larger tank as soon as my 30 gal display is full, and my thinking is that if I go ahead and setup a 30 gal sump/refugium now, I won't have to setup a new one for a larger tank when I buy it.  Here's where I am getting stuck, by reading the refugium FAQ's I have determined that the flow through the refugium should be around 3-6x. I can accomplish this with an Eheim 1048 (about 150gph) but I cannot find an overflow box rated lower than 300gph, which is almost twice the flow of the Eheim 1048.  What should I do here?
<Tee off the return line to feed the refugium.>
The design of the sump/refugium would have the overflow box feeding into a skimming chamber, where I will incorporate the skimmer, bubble trap going into the second chamber that contains the refugium, baffle going into the return chamber.  I've got the design preliminarily worked out, but how do I figure out how large the return chamber should be?  I want to maximize refugium space but not at the cost making the return chamber too small.
<Here is a link that will give you formulas to all your questions.
http://www.reefcentral.com/calc/hlc2.php  Look at the left sidebar, a list of calculators available is listed.  James (Salty Dog)>

Re: Sump and Return Pump Questions   2/14/07
Thanks for your prompt response.  I have a couple of additional questions.  I'm not great at math, so I would like to know if there is a way to determine how many gallons will drain from the (2) 1 1/2" overflows versus how much flow I will get from an Iwaki 100RLT (or one of the quieter models you mentioned....what pump would you recommend?).
<Mmm, there are useful approximations... much can/does affect such... issues of added plumbing, horizontal runs in particular... There is a semi-useful "calculator" posted on Reefcentral.com... In practical applications, providing for excess... occlusion... is wise. Our collective evaluations of pump choice are posted... here: http://www.wetwebmedia.com/marsetupindex2.htm
Do you see the links?>
How much of a turnover would you recommend?
<... also posted...>
I will be creating the reef with walls on the ends and an open swimming area in the middle.  Would I be better with 4 returns versus 2?  
<More than less>
I will drain each overflow separately.  Concerning the refugium in the sump, would you recommend that I place a piece of Plexiglas with a few holes in it so reduce the flow rate through the refugium?  
<Actually another bypass arrangement would be better... again...>
Do you have any additional suggestions?
<Heeeee! You're not joking I take it... sorry, just struck me as humorous>
  Would you recommend any wavemaking devices?
<Mmm, no... more gimmick than of use in most (small) hobbyist set-ups>
I would prefer not to add powerheads because I used to have a 150 gallon reef and every time I used a powerhead, it would run for a day or two, then the motor would burn up.
<There are better quality units... Look into Tunze here...>
  I sincerely appreciate your feedback.  I would much rather get things right PRIOR to establishing the tank.
  It will be much easier to do things right the first time than to correct them later.  Thanks again.
<Am in total agreement... Read... the Net, books, perhaps conferring with other hobbyists... a club? A guru there? BobF>
Scott

Sump Flow/Return Pump Selection - 12/07/06
I would like to add a sump to my tank and take off the canister filter.
<<A fine idea>>
I'm a little hesitant, due to the so called "flooding" in a power outage.
<<Easily managed/avoided with careful placement/positioning of overflow/return plumbing>>
My question is regarding the return pump.
<<Ok>>
My setup would be as follows for a 75 gallon FOWLR tank:
2 - Continuous siphon overflows (due to a non-drilled tank).
<<The redundancy is smart planning>>
600 gph w/1" outlets & 100 gph Venturi lift pumps.
<<I would only plan/expect to flow about 300-350 gph through a 1" overflow>>
1 - 12x12x24 tank for the sump divided into three compartments.
1st for the AquaC Remora Pro skimmer, heater & Chemi-Pure.
2nd for some live sand and rock with a compact light.
3rd for the return pump (here's were I am not sure).
My pump has to pump more than 1200 gph?
<<Mmm, no...the two 1" overflows will only handle about 700 gph combined before they become very noisy/a hassle to "tune">>
Do you prefer one kind over another?
<<I generally prefer a "submersible" pump for reasons of noise attenuation>>
Could you recommend one?
<<For your setup I would probably use a MagDrive 9.5 with a gate-valve installed on the output side of the pump to temper the flow as needed>>
I want to make sure I get the right pump the first time and not get one that might be under or over powerful.
<<I think the MagDrive (with installed gate-valve) would serve you well>>
Your help would be most appreciated.
<<Is my pleasure to assist>>
Would you recommend a spray bar, power head, or just the return flow on the end of the return lines?
<<You "could" use a spray bar along the upper-back of the tank, but I would probably just adjust/position the outlet pipe near the surface (to preclude back-siphoning too much water when the power is off) and pushing water along the length of the tank.  You could then position a powerhead on the opposite end facing the pump return for some random turbulent flow>>
If using one of the above, would I need the use of additional powerheads for circulation in the tank?
<<Additional flow is almost always beneficial>>
Maybe one or two on the bottom?
<<Wouldn't hurt>>
Thanks in advance for your advice.
<<You're quite welcome>>
I think your site is wonderful and I've learned a great deal in such a short amount of time.
<<Thank you...is a collaborative effort>>
I would love to get your book.
<<Bob has several, but 'The Conscientious Marine Aquarist' is a great addition to any marine hobbyist’s library>>
Dawn
<<Regards, EricR>>

Sump/refugium   11/24/06
Hello,
<Hi there>
            I have a question regarding a sump/refugium.  I have researched the site but haven't found any information on exactly what I would like to do.  I currently have a 55g with 55lbs of LR.  I have a 2.5in sand bed and I am slowly adding to it to increase the depth to acceptable DSB levels.  I have 2 Seio M620's and 2 MaxiJet 600's for powerheads, a Remora Pro, 1 blue damsel, 2 percula clowns.  I have decided to add a sump/refugium before adding more livestock but they both have to be upstream.  Here is my question.  I purchased a 29g tank and I was originally thinking that I would divide the tank in half.  I would put a 6" DSB, LR, and Chaetomorpha in the left half of the tank drawing water from the main tank through a mini jet 404. (I have tested this and I can get almost the full range it says on the box. I don't have to pump up more than 8 in.)  This would gravity feed through a 1" bulkhead back to the tank.  The other half would be the sump where I would store the Remora Pro, heaters, activated carbon at times, and a Magnum HOT at times, with baffles to reduce micro-bubbles.  I was thinking of a sock filter or something to catch larger stuff from entering the chamber.
<Best to situate/place this on/over a fitting inside the first chamber line on the inside... fed by the pump/powerhead>
I would also use a pump to draw from the display tank and a gravity feed back through a 1" bulkhead.
<?... as a totally separate process I take it... a "return manifold" to use the parlance. NOT in association with this upstream refugium>
I have read that a 1" bulkhead is realistically good for 200gph.  I will figure out what size pump to buy for that but here is my question.  Would it be better to design the sump/refugium like I explained above so that the fuge and sump are fed separately at different flow rates or would it be better to incorporate the fuge into the sump using 1 pump and 1 gravity feed back to the display?
<This latter... one pump... not two here>
Your site is incredible and filled with an unbelievable amount of good information.  There would be many aquarists who would have given up if it wasn't for your website and the time your crew has spent in answering questions.
Thank You
Paul Kelly
<A pleasure to serve, help you in your successes. Bob Fenner>

Small Bubbles from Sump Return Pipe – 11/01/06
Hi Eric,
<<Hey Ken>>
I have an annoying dilemma.
<<Uh-oh>>
Would you have an opinion as to what is causing small bubbles coming out of my return pipe into my tank?
<<Sure...I have opinions on most anything <grin>.  It is likely you either have a very small plumbing leak that is “sucking” air...or the return pump is pulling bubbles from somewhere in the sump>>
It has been like this since the first day.
<<A very common issue>>
I was told last week by someone that it was probably because it was new sea water in the tank.
<<...!?  I don’t think so>>
However it is still occurring.  As you know my tank is a 90-gallon AGA mega-flow tank which has the internal skimmer box.
<<Yes>>
I put saltwater in it 8 days ago.  6 days ago I added about 120 lbs of live rock.  I have a 48” MTC Beckett style skimmer coming off the other side of my sump which has two baffles.
<<Have you checked to ensure the baffles are keeping bubbles away from the return pump?>>
When I look closely at the return to tank side of the sump, I really don’t see any bubbles to speak of so I do not think that this is the reason.
<<Ah...ok>>
Also when I shut the pump off and turn it back on, a lot of large bubbles come out of the pipe going into the tank.
<<When the pump is off the return line drains, yes?  The “large bubbles” would be the air that is pushed back out the pipe when the pump is turned back on>>
Is there air in the system?
<<Possibly from a small (pinhole) leak at a connection/union>>
The water flow from my sump to my tank is as follows:
¾” pvc flex tubing into ¾” union >>> Blueline 40 pump >>> 3/4” flex tubing  >>> bushing to increase to 1”>>> 1” ball valve >>> 1” union >>>1” ball valve >>> Bushing to decrease to ¾” >>> ¾” PVC >>> two 90 degree ell’s into my chiller >>> two 90 degree ell’s from my chiller >>> ¾” flex PVC into the bottom of the tank for the return.
<<Lots of joints...you need to check each one of these (that is “out of water”) to determine if one is “leaking” air in to the system.  You can smear Vaseline around each joint, though this must be “cleaned carefully” to keep the petroleum component from deteriorating the plastic (Bob does not recommend this method), or you can get a silicone grease for doing this.  Seal each joint one at a time, waiting a few minutes each time to see if the bubbles stop>>
The other problem (and maybe related) is that when I put my hand in front of the return line into the tank, I hardly feel any flow.   The Blueline pump is rated at 790 gph @ 5’ head.  I used a head loss calculator and I should have at least 560 gph.
<<Did you also take in to account the turns/valves in the plumbing?  Each 90-degree ell adds a foot to the head height, and I would also add a foot for each ball valve in the line...the unions and the chiller will be adding some additional resistance to flow as well  All in all, you will likely find the pump is less adequate than you thought for this installation>>
I am not sure what that feels like against my hand, but it has to be more than what it seems.
<<Only way to know for sure is to direct the output in to a container of known capacity and time how long it takes to fill>>
I appreciate at any idea someone may have.
<<Hope I’ve given you a few>>
Thanks,
Ken
<<Regards, EricR>>