# [Wet Thumb Forum]-Water heating problems with my PC lights



## imported_Mike (Feb 7, 2003)

I've recently set up a 75 gal tank with three 96 watt power compact lights giving me 3.8 watts per gallon. Of course, the metal hood is retrofitted with these lights. The problem that I am having is that the lights heat up the water from 75 to 83 degrees during the day. The lights are not enclosed in anything and beam directly down on the water.

I've thought of placing a glass top on the tank that would be 2" below the pc lights. I'm sure this would help, but will I lose much in the way of lumens to the plants? Also, should I use some kind of temper glass or is conventional glass okay? In theory, I could place electric fans on the back of the hood, but it would be tricky with the metal construction of the hood and I would like to avoid more noise with my tank. The fans would keep the bulbs cooler, but would they really keep the water from heating up?

Any comments, feedback, helpful hints or tips regarding this situation would be appreciated.

Mike


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## imported_Mike (Feb 7, 2003)

I've recently set up a 75 gal tank with three 96 watt power compact lights giving me 3.8 watts per gallon. Of course, the metal hood is retrofitted with these lights. The problem that I am having is that the lights heat up the water from 75 to 83 degrees during the day. The lights are not enclosed in anything and beam directly down on the water.

I've thought of placing a glass top on the tank that would be 2" below the pc lights. I'm sure this would help, but will I lose much in the way of lumens to the plants? Also, should I use some kind of temper glass or is conventional glass okay? In theory, I could place electric fans on the back of the hood, but it would be tricky with the metal construction of the hood and I would like to avoid more noise with my tank. The fans would keep the bulbs cooler, but would they really keep the water from heating up?

Any comments, feedback, helpful hints or tips regarding this situation would be appreciated.

Mike


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## Avi (Apr 7, 2004)

If the bulbs which are the source of heat are two full inches above any glass that you might put on the top of the tank, it wouldn't have to be tempered glass though for peace of mind you could use tempered glass. Of course you would lose some lighting strength, but if the tank isn't taller than 18 inches it shouldn't be a problem...make sure you clean the glass regularly. I wouldn't fool with putting electic fans into a metal casing...unless you really know what you're doing.


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## lsuber (Dec 15, 2003)

I'm having a somewhat similar problem with my 90-gal tank. I DO have glass tops/covers on it, and my temp rises from 80 during the night to about 83 during the day. I'm not sure if that's really significant or not in terms of the tank's overall health. For your comparison's sake, I have 220w over a 90-gal tank with glass tops, so they might not prevent your 75 tank with 288w from heating up.

I'll be intersted to see the other responses here, and to find out if my 3-degree rise during the day really matters.


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## imported_Mike (Feb 7, 2003)

Isuber, I wouldn't think a 3 degree change would be that much for concern unless your top end temperature goes up further during the summer months. I'm afraid the 8-10 degree swing that I'm getting is too much and we're not even into the summer months.

By the way, my tank is 20" deep and I have black gravel.


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## Southrock (Feb 3, 2003)

I've also had the same issue with 6 96w pc bulbs on top of a 180g tank. The tank originally had a glass top covering it, and the lights are in a hood about 5 inches away. The water temp would get as high as 88. The glass top actually created a sort of convection oven.

So I removed the glass, and now the temp remains a manageable 84.

I guess what I'm saying is that IME, putting a glass top on the tank might actually make the water warmer.

The fan idea is probably a good idea, the metal hood could make it a little tricky. It might be a good time to know an electrician!

Good luck.

-SR


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## Rex Grigg (Jan 22, 2004)

Vent the hood!










American by birth, Marine by the grace of God! This post spell checked with IESpell available at http://www.iespell.com

See my Profile for tank details.

See my planted tank FAQ at http://members.dsl-only.net/~rex/
Caution, contains content which will offend sensitive people. Rated PG 13


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## imported_Mike (Feb 7, 2003)

Any suggestions as to what type of electric fans to look into for installing in the hood?


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## Southrock (Feb 3, 2003)

You could go to Radio Shack and get one or two of those computer cooling fans, 12v.
I went to a hardware specialy store "Grainger" (don't know if they have those where you are). They range in sizes measured by volume of air moved, ie. 14 cu ft per min. All are 12 volt - I use a doorbell transformer to bring the 120 down to 12. You should be able to find them at any hardware store.

Don't forget the elecrician friend!









-SR


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## JamesHoftiezer (Feb 2, 2003)

When I was setting up my tank there was so much talk about heater I never thought I would overtemp the tank with the lights. I have 330w over 100g.

In my case I have added two pieces of glass directly under the lights that still leave about 1/3 of the surface area open. I then added several low noise 12v fans. You can buy them on line for $7-10 each. Most people will get 80,92 or 120mm. You can get fans deemed low noise or silent fairly easy now.

The 12v fans will require a 12v transformer. I got mine from radio shack for ~$13

*James Hoftiezer
Hoftiezer.Net - Journals and Libraries
Rate My Tank!!

Tank Journal - Aquascape ( Latest / Archive(No Longer Active))
Tank Journal - Parts and Construction ( Latest / Archive(No Longer Active))*


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## JERP (Feb 4, 2003)

The only problem I have had is overheating the glass lid. The glass lid can crack if water splashes on it. You can raise the lights, or add fans.

How do you know if you have a problem? Touch the glass. If it seems uncomfortably hot, then you might have a problem.


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## imported_Mike (Feb 7, 2003)

Thanks everyone for your feedback. It looks like I'll have to do a combination of glass lids and adding fans.

James H., I checked your parts and construction link, but, it didn't go through to anything. Could you or others mention some web sites that I might check for purchasing fans?


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## imported_Mike (Feb 7, 2003)

I've been checking other threads in which people are talking how they lowered the temp of their tanks by 1-2 degrees by adding fans. This seems hardly worth the trouble of adding the fans. What have been you guys experience with the fans?

Also, James H., what was your rationale in keeping 1/3 of your tank uncovered by your glass cover?


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## Tenor1 (Mar 3, 2003)

The fans help extend bulb life by dissipating moisture and heat. I think there is little effect on the water temperature. 

Rex offered the most practicle solution of creating vents. It might be easier-said-than-done for many hoods, lol. I wish more manufactured reflectors like JBJ, et all, designed much larger vents on the units. I personnally don't like the fan noise plus there are many units with broken or extremely noisy fans. 

Regards,
Carlos

==============================
I try to keep the tank plain and simple but it never stays that way!


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## JamesHoftiezer (Feb 2, 2003)

I dropped my temp by 4-6F with fans.

I only have 1/3 of my tank covered because;
a) it was an afterthought
b) it was easiest to have two smaller peices of glass made than a big one
c) the smaller glass is easy to move around and functins as a work bech during prunings
d) I have some cables and equipment going over the edge.
e) The fans pull heat from above and below the glass
f) since heat is the issue, I didn't want to create an insulated layer which would be heated by the lights increasing the water temp

*James Hoftiezer
Hoftiezer.Net - Journals and Libraries
Rate My Tank!!

Tank Journal - Aquascape ( Latest / Archive(No Longer Active))
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## gsmollin (Feb 3, 2003)

I think the rationale for adding fans is to lower the lamp temperature, not the water. The water is primarily heated by the radiation from the lamps, while the fans increase convection cooling. Of course, some of that heat in the hood radiates into the tank as thermal infra-red, and conducts through the glass, so yes, adding fans sounds like a couple of degrees to the tank water, but 10-15 degrees inside the lamp hood. In a dense lamp hood, that could be an important difference. My lamp hood runs at 70 degrees Celsius = 158 degrees Fahrenheit, which is the upper limit for fluorescents. I have only 2 W/gallon. If I went to 4 W/gallon, the hood would require forced air cooling to prevent overheating.

Removing glass from the tank top is an easy way to cool the water by evaporation. You can still keep a glass cover on the lamp hood to protect the lamps from water. Expect to add gallons of makeup water weekly. With weekly water changes this is pretty painless.


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