How low can I mount my lights (New Tank)

[Bayliner]

Hi,
I am starting up a new 75g SPS tank.
My fixture has 2-250W MH bulbs and 2-110W VHO bulbs.

I used to run this fixture on my 90g 25" tall tank resting on the top of the tank with good results.

Now that I have a 75g short, only 20" tall can I still do this ?
Or should I raise it up 5" off the top of the tank ?


Thanks
Cam

[StrategicReef]

you can run it as low as possible.

[elijaher]

Hang your light about six to nine inches frome the water. You don't want to heat up your water to much you could also bleach your corals.

[JustinReef]

I keep my halide about 1 1/4" off the top of the water. I have had some reflectors that are better higher up like 12" off the water. All depends on the reflector and your preference.

[elijaher]

You can always bring it down later. I have mine seven inches but planing to bring it down close as possible.

[sedor]

Heat is your main issue. The air between the water and the light doesn't change the PAR very much. If it worked resting on the tank on the 90, you could probably get away with it on the 75, especially if the fixture has fans in it.

[Bayliner]

Thanks for all the info everyone.
I am building the stand and hood today and I needed to know this before I start.

I will build the hood with enough room to start the fixture up 6" and make it adjustable so I can lower it all the way down if needed.

Thanks again for your advice,
Cam