Help! Lights cracking my glass tops (?) - The Planted Tank Forum
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post #1 of 10 (permalink) Old 08-16-2011, 02:33 PM Thread Starter
Join Date: Aug 2011
Location: NJ
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Help! Lights cracking my glass tops (?)

Help! My custom cut glass tops for my aquarium both cracked. I believe it is from the heat of the lights but you tell me. Am frustrated. I don't mind spending the money to get new tops made, or to buy different light fixtures, but I want to understand what happened, and what I'm doing wrong, to get it right next time.

Photos of my setup are attached, showing the tank, the lids and lights (one stacked on top of the other just for the photo so you can see the lid, and one with a closeup of the crack).

Let me ask my questions first, and then I'll give all the detail below for those interested. And thank you in advance for your help! These forums have been great.

1. Is it OK to place aquarium lights right on the glass top? I thought so, but maybe not.
2. Check out the cracks here in the photos. Do you agree caused by heat? Maybe glass corner notches for piping weakened glass too?
3. Can you recommend a different kind of lid, or lights, to avoid cracking? Maybe light fixtures that run much cooler, even if they won't work for plants?
4. Any risk the lights could crack the glass bracing on the tank itself? A terrifying thought!

My tank:
- Custom sized 68 gallon. 5 feet long, 1 foot wide. Basically it's a standard 55 gallon stretched to be 1 foot longer. That was my first mistake. Custom tank size means custom lids and that is the root cause of my aggravation.
- Fish: regular tropical freshwater fish assortment
- Plants: none yet. was thinking about it, which is why I got the lights I did, but am reconsidering...
- Lights: Deep Blue Solarmax T5, two 24" fixtures, each with two daylight bulb tubes inside. It does get hot when both are on. See link to fixture here:
- Glass lids: were custom cut of 1/4" regular glass, with corners notched for tubes / wires. Front piece is acrylic flip up lid for daily feeding access.

Basically, because of the custom size, I had to get custom lids made. Major pain. But I finally got them right, with notches for tubes. Then I set up my lights, and after running both lights, both lids cracked! Sigh. If I raise the lights up off the glass (3/4"?), using the metal extenders on the side of the lights, then a lot of the light leaks out the back of the canopy (see my first photo of my tank showing this), and presumably less gets into the tank.

What I wish I could find, or have made, a durable (plastic?) lid fixture that would fit the light inside of it, so I didnt need to have a glass top at all. But the overall sizes I would need are about 25.5" by 10.5" for each lid, which is not standard. That's coming from a person who upgraded from a basic 20 gallon tank that had an integraded canopy / light / lid / door which worked great. Really wish I had stuck with a standard size tank.

Any advice much appreciated, thank you so much!

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post #2 of 10 (permalink) Old 08-16-2011, 09:30 PM
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Location: Monterey, CA
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Looks like the notch/corner chiseled out of the pane definitely was the weak point. Generally, glass won't crack from (even) heat by lamps, more likely that the whole fixture will melt into a bubbly mess before that happens. Now if (when) cold water splashes against the hot glass, then we might have a problem.

T5 fixtures are often "cooler" running compared to PC fixtures and HQI's. Of course it all depends on ventilation. If you feel your fixture is overheating, adding a fan or two to it might be a wise decision, not so much for the glass, but to extend the lifespan of bulbs and fixture, and to keep the heat transfer to the tank under control.

You could add an acrylic panel (or two) to the bottom of your fixture via some sliding tracks, but that comes with a different set of issues.
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post #3 of 10 (permalink) Old 08-16-2011, 09:41 PM
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Location: El Paso, Texas
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I have a 96 watt cfl on my 46 BF. The top glas did break on me one, and I’m sure it was from heat trying to escape. I raised the hood by ľ” and haven’t had a problem since.
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post #4 of 10 (permalink) Old 08-16-2011, 09:55 PM Thread Starter
Join Date: Aug 2011
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thank you

Thank you for the feedback so far. Yes, agree the notching of glass probably contributed.

One person suggested switching to LEDs, or traditional fluorescents, and said both a lot cooler than T5s. Any ideas which runs cooler of those two?

Any and all input much appreciated.
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post #5 of 10 (permalink) Old 08-16-2011, 11:16 PM
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I always have a small fan blowing accross my T5 fixures. Keeping them cooler can also help the ballasts and the bulbs last longer.
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post #6 of 10 (permalink) Old 08-16-2011, 11:26 PM
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What about cutting an acrylic lid? You might even be able to buy a sheet and cut it yourself. You'll definitely have less of a worry of cracking due to cold water splashing on it.
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post #7 of 10 (permalink) Old 08-17-2011, 12:54 AM
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I had a PC unit on the glass and it cracked the glass where return water splashed on to the glass.
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post #8 of 10 (permalink) Old 08-17-2011, 06:57 PM Thread Starter
Join Date: Aug 2011
Location: NJ
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Thank you all. I've thought about acrylic, but heard it will definitely sag and quickly so not so good esp. for a wide span. Other people have recommended Lexan (like acrylic but stronger?), or "eggcrate" mesh used in ceiling light fixtures (rigid and cheap, stops "jumpers", but wont stop splashed).

At the moment I'm thinking about the following solution:
- New glass tops, but maybe with plastic piece in the back so I can cut notches in that, and not have to notch the glass (like the glass "Versatops" product)
- Maybe upgrade lighting to LEDs. Supposedly run very cool. "Ecoxotic Stunner Strips" were suggested and seem to be well regarded.
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post #9 of 10 (permalink) Old 08-17-2011, 11:00 PM
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I would replace the glass and put the fixture on legs.
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post #10 of 10 (permalink) Old 08-17-2011, 11:50 PM
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I would make the next glass with a quarter round cutout instead of the rectangular one, to eliminate the stress concentration at the corner of the cutout. Then raise the light a few inches on legs. You could also have the glass tempered after the cutting is all done, to make it more resistant to the heat. (If it does crack it will shatter into lots of very small pieces, so that might not be a good idea.)

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crack, glass lid, glass top, lights

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