DIY Light Hood…Where Do The Fans Go? – 08/11/07
I built a custom 200-gallon salt water tank approximately 8ft wide and 2ft deep with PC lighting on the hood. I bought 2 fans, should they be installed on the sides, the back or the top, and where should I place vents on the hood?
<<Any of the placements you mention will work, with the “vents” placed distal from the fans to promote air flow throughout the hood. Most DIYers position the fans/vents with an eye toward aesthetics so really, the choice is up to you. And if you want to limit the number of holes another option is to place a fan on one end pulling air out of the hood, and the other fan at the opposite end blowing air in to the hood. EricR>>

MH 175 and enclosed canopy
Bob, I have not asked anything of you as yet.
Now, I may be getting into trouble.
I have built a killer lower canopy for my 125 all glass (about 16 in. high), with large doors that keep *all* light from escaping and easy access to the reef. This thing will also slide forward, so that I can service the overflows, etc.
<Sounds very nice>
The canopy is in two parts and of abs plastic. The top ( or lighting part) is a work in progress.
I have a limit switch to cut off the 175 MH lights at 160 degrees that I can place at the hottest (or any) part of the upper canopy and a 130 make/ 90 break snap disc control for the two 4 in. RS, 115v fans. 
<Have your later input re the lower limit (110) for the high shut off>
Lighting will be, two 175 MH, four 4 ft (40 watt) and two, 3 ft. tubes. By the way, those (White-Rodgers) snap disc controls are great and available from Grangers <Grainger> for only 7 to 8 bucks each and I have tested them for several hours, but not on the canopy !. The limit switch will take care of up to 10 amps and I chose the (3L02-161) with a manual restart instead of an auto restart. I figure that if it cuts the hot lights off, there is a good reason and the problem needs to be corrected prior to switching back on.
<Yes>
My thinking on this project is to keep it light weight so that I can remove it without help and I hope to be able to use a lightweight acrylic shield between the two canopies as I wish to avoid heating up my tank.
This same thinking is the reason, I do not wish any motor in my sump or in the tank.
I am running two Quiet ones and driving the skimmer and the 5 nozzle water movers that are in the lower part of the tank and behind and between the live rock off of one pump. The upper supply (six directional nozzles) are on the other pump.
The two fans are both blowing in and can be partially directed at the acrylic sheet, below the MH lights
<An acrylic sheet below the lights? I would not use one here... and want to mention/ask that you have heat and light deflectors as part of the fixturing above, separating the MH lamps from the ABS sheet plastic making up the canopy?>
This should not cause much pressure, because I will have some holes in the top, covered by a four foot by one foot, black plastic roof heat dissipater from Home Depot, on top of the light canopy.
<On top... but also something inside... deflecting the heat from the structural hood>
My question (before I get further with the upper part of the canopy), is...
How close to those 175 watt, 10k MH lights, can I place the acrylic lens?
<Were these supplied as part of the fixture? As UV filters? To protect against touching, splashing? If so they should be mounted per the fixture. If not provided as a component, I would mount the lamps at least a foot from the waters surface, sans any in-between material>
Do you know at what point the would start to deform, melt or bend etc.?
<Depends on some properties of the specific make-up, thickness... likely not too far from just being near the lamps... in the mid to upper 100 degrees F. Do take care here, contact the dealer you bought these units from. Am cc'ing Dave Adkins here. Dave? Bob Fenner>
Thanks,
Dave Moose

Re: MH 175 and enclosed canopy
Thanks Bob and hi Dave,
ABS and Metal Halide in the long run is scary enough. Are you using 1/4" or thicker?
What size tank is this?
I guess I'm reading that you have an entire closed hood? The only air moment is the two fans?
If you contact someone on the ABS/manufacture to discuss thickness vs. melt down you can come to some conclusion on what to expect.
The general rule on Metal Halide temperature is the old rule of thumb which states for every watt is an element of heat.
Hope any of this helps.
David Adkins
<Thank you David... oh same fellow as Aquariumlighting.com for you all>

Re: MH 175 and enclosed canopy
Thanks for the reply, Bob. (and Dave)
One thing is very apparent to me now. I did a sorry job of depicting for you, just what it was that I built for this 125 gal tank.
No one sold it to me, so, I can't put any fault on anyone but me.<g>
The top canopy (the part with the lights, fans and thermostats and limit switch with the smaller electronic ballasts on top of it) is only 10 inches high and sits on the 3/16 in. acrylic sheet, which is inserted into the top of the bottom (larger) canopy. The MH ballast of course will be separate from the sump area and the canopy.
This was sealed in such a way, that the water (or air) from the lower, or main canopy, cannot get to the light canopy except (perhaps) via the fans on each end. But even then air and water would have to travel 13 inches around a corner and up about 20 inches more.
I know that you have been saying that nothing should be between the lights and the water, but I have found , prior to building this thing, that fans on water a lot of heat is a sure fire ticket to massive and constant water additions 
<And waste heat reduction>
and if not watched constantly, the relative salt content of the remaining water, will increase too much. Not to mention the effect of up to 600 watts of light on the temp of the reef.
The acrylic (if it works) will stop all (or most) of that.
<But... the acrylic will reflect an appreciable amount of light... and alter spectral penetration...>
This acrylic is more optically clear than glass.
<Than some types of glass>
I do have (in addition to the mirror finish aluminum above the MH lights) some "Bobcat White" painted aluminum 1/16 in. ionized sheets between the retro mirror finish aluminum and the ABS and stood off from the ABS with 1/2 in inch nuts, as a heat sink and shield, with the holes for escaping hot air at the sides and in places that any lights can still reflect downward.
<Ah, sounds like a good design>
I have just finished testing a half hour ago, with only the two MH (on the back deck <g>) and the fans did not even come on. Of course it is a little chilly out there. I am beginning to think that it is going to be relatively safe (as far as any heat is concerned) to go ahead and place the other lights in there tomorrow.
My concern now is twofold. One, the phase/color shifting your talk about and, the other concern is what happens to the thin but well supported acrylic when about 600 watts of light hits it, even if the fans and the attic heat dissipater is working fine.
<Only way to really tell is to try it out... you might want to mount a thermometer on the acrylic sheet for a test run... while you're still present... and see if the sheet approaches the flash point>
I could of course had one blowing in and the other out. But, I tested that two days ago, using some military fog and noticed that there is only a funnel of air going in and out and not enough turbulence in corners and particularly on the acrylic shield. I think that I like the effect of the fans blowing in and forming a pressure that escapes from the top. An air condition engineer friend told me that I should have both fans blowing in from the top at each end and then dispelled from the roof ridge thingy and that would cause the most turbulence and coverage.
<Interesting>
But, I didn't like the thing bringing in air that had just been dispelled.
As usual, I tend to "over engineer" and trying my best to idiot proof this (good looking) monster.
Thanks much for any input or even telling me that I a dead wrong. I am continuing to study the problems involved in having something between the lights and water.
To be safe (I think) I can keep this light canopy to a safe temp. These two 4 inch fans move a lot of air in a sealed container that is letting air out only at the top.
I think the ABS stays structurally sound to 200 and the acrylic to 160 or more.
I think I can stay well below this.
<Not so sure re the acrylic here>
I say that I think !.
In any case, I will test the whole thing over the next few days (weather permitting), on the driveway behind the house. <g>.
I can add more fans (if needed).
I could of course just remove the acrylic and have the lights about 20 some inches from the water.
<I would take off the acrylic for sure. Who can say as it gets older, dirtier, the ambient temperature gets warmer, if it may ignite.>
By the way, I have also built a 12 by 2 stand and reservoir that the tank
cabinet is sealed to, and sits on. Just as an additional protection against the 30 gal sump or pumps malfunctioning.<g>
This helps also, in that you do not have to bend over to watch the tank critters and rock.
This tank is only 4 months old and the live rock is doing cured and a ton of discovered critters and new ones every day are being found in the rock. I am just getting ready and looking forward to adding some light loving coral etc.
Thanks for any all help, I am learning and you guys have been where I am traversing.
Dave Moose (in North Carolina)
<Be chatting. Bob F>

Re: MH 175 and enclosed canopy
> The acrylic (if it works) will stop all (or most) of that.
> <But... the acrylic will reflect an appreciable amount of light... and alter spectral penetration...>
Not only that but in time you will have yellowing, most acrylic will bow with moisture and because "things happen" will apply you/animals will start putting small little fine scratches that will now trap salt creep and or algae.
It sounds like you did a lot of research and thought into you lighting set up. Please keep me/us informed as time goes on. Who knows you may have designed a hood that will with stand time and thus we will be able to pass on your findings.
David Adkins
<Ditto! (Always wanted to write that, and need to send self a copy for posting for browsers). Be seeing you David. Bob F>

MH 175 and enclosed canopy (part 2)
Mr. Fenner, I made a error in my first mail to you.
I said that the fans were on a thermostat that was "130 make/ 90 break".
The thermostat is, in fact, 110 and 90.
Sorry !
<No worries>
I didn't know how to post to your site, so I just sent the e-mails.
You may post them on your site if you wish. Or not, if you care not too.
I do love reading your answers to other's problems.
Thanks so much, for being so much help to all the folks.
<And you for your help, input. Bob Fenner>
Thanks,
Dave Moose

-Mounting fans in canopy-
Dear Crew I just received my MH/PC retrofit. I also bought 2 Ice Cap fans.  My question is this: What is the best way to place them?  One at each end of the fixture? Across from each other?  What?
<One on each of the long ends, one blowing in, one blowing out. Good luck with your new lights, and enjoy the new found heat! -Kevin>
Marion

Re: Questions about lighting for new tank
Ok I can do the metal halide instead of the PC, I was looking at a 2X175W MH
retrofit as well (costs a little more but if I can keep it cool without a chiller I'd consider it). <Fans will do the trick, you'll need to get some large ones installed in the hood to keep it cool> But I was concerned with the heat since I will be keeping it under a canopy.  Is it possible to cool the lights enough with fans that it won't raise my tank temperature and also not set fire to my wooden canopy and burn my house down?  And if I did the MH then the two VHO would most likely be Actinic correct?  <Definitely> Thanks for your previous reply and advice, Clif <Good luck Clif, MacL>

Lights, camera, fish tank!
Dear Wise Ones,
<That's Wise Guys to you!  Ha!>
I'm setting up a 220 acrylic reef tank (72'"x24'"x30") in my living room, with sump & mechanicals directly below in basement. <Very nice.  Eliminating noise, sloshing buckets and siphon hoses form the living space dramatically increases spousal acceptance factor!>
In order to accommodate the necessary lighting, I'm having a 14" deep canopy constructed. My issue: I wanted to use three 400w M.H.s plus VHO blues, but my supplier says that there will be too much heat in the enclosed canopy, even with 4'" fans (and 1/3 hp chiller).<Heat will be a concern.  Consider bumping up the number of fans and/or using an exhaust fan that will carry the heat out of the living space (into an attic or outdoors).  A 1/3 HP chiller should be adequate if you take steps to move as much heat out of the hood as possible, otherwise, jump up to 1/2.  Since you will be in the basement, you could also consider some alternatives like running your R/O input through a long coil in your sump.  This will warm the water for the R/O (improving efficiency) and cool the tank.  If you have a sump pump, the sump makes a great geothermal heat sink.  Be creative!>
He recommends three 250w M.H.s and four 96w blues. This seems a little "light" on light (sorry, couldn't resist), especially for the few SPS corals I will be transferring to the new tank. Your opinion is highly valued! Patrick  <The difference between 250 and 400w MH in terms of actual light output is not that great.  If you choose 250w DE along with their super effective reflectors, the difference becomes very small.  With either 400w or 250w double ended, you will have plenty of light in the top half of the tank for just about anything.  If you go with all 400's, you may have trouble finding spots for those lower light critters like Euphyllias, etc.  Bottom line...  IMO, 400w are probably over kill unless you want to keep light demanding SPS low in the tank.  As a point of reference, I am growing Acros, Montis, etc. even low in my 24" deep tank that is lit only with four VHO's.  Good luck!  AdamC.>

Lighting Quandary...Part II
Okay, one follow up question then.  I have a canopy on my 55 gallon tank and my wife and I both really like the way this looks.  If I were to go to a pendant system, can I mount them in a canopy?
<If there is enough clearance and sufficient ventilation and fan cooling, you can definitely do this. I have pendants mounted in the canopy over my reef system.>
Will I need to worry about temp under my canopy and possible overheating.  (I may already have a problem since my current temps in the summer for Freshwater run in the low 80s for about 3 months.  I'm looking into fans to see if that will cool the water enough to get it back down to about 79 degrees.).  What do you think?
<Well, cooling and ventilation are huge issues when mounting pendants in the canopy. My canopy was designed specifically for pendants; you may need to see if yours will work. You should allow at least 6-8 inches of clearance above the water, and a little more room for ventilation.>
Thanks again for your input and support of all of us that are trying our best to learn what we need to keep these beautiful and fragile creatures in our homes and under the best possible conditions!
Jeff Smith
<Glad to be of service, Jeff! Good luck! Regards, Scott F.>