MH Halide Clearance

[ice-qube]

Just wanted to ask you guys about what is the neccessary clearance needed for a MH bulb from the water?? My tank is a 40 Gallon square tank. 24"X24"X18" . With the sand and water not filled to the top I have about 16.5" water depth. Am I looking at a possible heat problem?

Also the MH pendant is just going to be going on top of my custom made wood hood with a hole cut out of it. Am I looking at a fire hazard? Or is the 175w bulb not going to get hot enough for a concern? (Only the outer edge of the pendant will lie on the hood). I guess I can always hang it to the ceiling and just have it hover overtop the canopy.


Q

[ajx22]

That's going to depend on a few things.

I have 2 175watt - 5500k MH's in my hood on my 100Gal. The lights sit about 10"-12" above the water surface, but still can raise the temp of my tank from 80 to 85 in a matter of 3-4 hours. I have placed a fan in my stand blowing directly on my open sump, and this has worked to keep my temp in check (though I'm topping off evaporate more now). :rolleyes:

You want the MH bulb high enough that water splashes/bubbles will NOT hit it. When salt water hits the HOT bulb, the water will evaporate quickly, and leave a salt deposit - which will heat up much more then the rest of the bulb. I've seen bulbs caked in salt still working, but it's not good.

As for the heat from the pendant causing a fire hazard; is your hood treated or just stained wood? I would place some kind of reflector around the hole, and hang the pendant. This way it will help disapate the heat, and you will still have air flow around the exterior of the pendant.

Just what I would do...hopefully some more folks here can post their thoughs on this too!!

Good luck,

[ice-qube]

Well the pendant already has a lens on it, that should keep any splashing of any kind. The actual clearence from the top of the water to the tip of the bulb ( which is screwed in vertically) is about 8". My real question is that does the water get hot from the heat eminating from the pendant or from the light hitting the water? or both? Reason why I am asking is if its the heat comming from the pendant I can have a fan blowing on it. But if its the water then I will have to look at cooling the water somehow.

To cool the water down, can I just have a power head pump water into a hose which will run along the floor in my basement, which is pretty cool. And then will just come back? I figure the hose could be 12 feet or something, which should give it sufficient space to cool down. What do you think?

[ajx22]

The water will get heated from both. If you can position a fan blowing on the MH fixture and the waters surface, this would be best.

Do you have a sump? If you do or decide to add one; the added water volume will reduce the amount of heat build-up.

The hose idea may work, but you will have to be sure that the hose material is potable (will not leach chemicals, etc. into the water). Also, you may find that a larger pump than a PH is needed too. One other thing to worry about, is algae build-up in the hose. If you use clear soft PVC hose, you will be able to see any algae blockages, but at the same time, by it being clear it will allow light into the hose to add to the algae growth.

If you're going to go to the effort of this pipe idea; you should look into the sump (assuming that you don't have one) addition, as it will help with heat, circulation, water volume, and will keep things cleaner in overall appearance too.

Does this help you out any more?

Hope so,

[Dman]

I have a 250W Iwasaki over a 50 gallon (36*18*18) the distance from the bulb to the water surface is about 8 inches with no protection, I have not had a problem with splash so things have been good and my temps are a a steady 82 degrees F.
HTH
Derek

[Dman]

Moved to Reef Discussion
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