Light Suspension Height

[Aquatic-Obsession]

Hey guys,

Just picked up my first metal halide light but i'm not sure how high to suspend it over my tank? It's a 20 gallon Long, and a 175w Metal Halide. Any advice would be greatly appreciated. Thx in advance

Alex

[RonPeter]

I keep mine about 10" from the water.

[danny zubot]

It really depends on your reflector too. I have a 400 watt MH with a crappy reflector so i'm not getting the light output I should be. Consider that a reflector runs on a similar concept to a magnifying glass. You can change the intensity or spread of light depending on the reflector and the hight above the oject you intend to illuminate. My sugestion is to play around with it until you find your "sweetspot".

[TheReefGeek]

It depends on if this is your first light, or upgrading.

If you are upgrading from say PC or VHO, then start with it higher up than 10", then lower it down over time.

I would also only run the MH for say 6 hours, increasing an hour a week to help the coral aclimatize to the new light.

I run my metal halides about 15" above the surface of the water.

[outtafocus]

Why do so many people run their MH so far off of the waters surface.
I have my 150w about 2" above the tank and I do not experience any heat issues.

My corals never seem to take off like others I have seen, is it possible that I am too close to the water?

I find if my light is much higher I get a lot of shadowing in the tank.

[christyf5]

I have mine about 6" off the waters surface, mostly I was more worried about splashing the bulbs, plus the tank stand is pretty high and by the time I got the hood on there was only a few inches before it hit the ceiling (low ceilings in the basement) so mounting them higher wasn't an option for me (not that I would have done it anyway )

[mr_alberta]

You will get more spread with your light the higher you mount them, but you reduce the intensity of the light the higher up you mount them. Mine are about 6-8" away but my lumenarc reflectors still put a tonne of heat back into the tank.

[christyf5]

Originally Posted by mr_alberta

but my lumenarc reflectors still put a tonne of heat back into the tank.

Crud, I was hoping you wouldn't say that Good thing I have my chiller.

[TheReefGeek]

I have mine that high up so that I can work on my tank. My light is suspended, but stupidly I didn't put it on a pully system, so height adjustment is not easy.

If it was 6" above the water, I would have to move the lighting every time I wanted to put a frag in, or target feed, etc. And hoisting a 6 foot long lighting hood is anything but fun.

Once I get my pully system running, then I will run the bulbs 6-8 inches to get more intensity, but avoid some splashing that might burst a bulb.

[Delphinus]

Originally Posted by outtafocus

Why do so many people run their MH so far off of the waters surface.
I have my 150w about 2" above the tank and I do not experience any heat issues.

My corals never seem to take off like others I have seen, is it possible that I am too close to the water?

I find if my light is much higher I get a lot of shadowing in the tank.

Remember though, 150W lamps put out only a fraction of the heat that larger wattages will. Plus, I'm assuming you're running DE, which means your fixture will have a cover glass. Most assuredly any unsheilded lamp at 2" above the surface will eventually crack due to splash.

Anyhow in answer to the original question, I run my halides about 6" off the surface too.