Height for MH lights

[ron100m]

I have a 200g with a canopy, 4 MH, light fixture. How high, or what distance should this be from the water surface?
Thanks

[sabbath]

About 8" from bulb to water surface.

[sabbath]

Oh just noticed. Welcome to REEF CENTRAL!!!!!!

[frederickk]

Mine are at 9''

Welcome

[jer77]

hey ron100m,

[welcome]

Are the MH's SE or DE? I find That most people have them at 8-12''. Mine are close to 12'' cause they are DE, they seem brighter and bleached some coral.

[bertoni]

A lot depends on the animals that are kept. I have kept halides anywhere from 3" to 8" or so above the tank. If your corals aren't accustomed to bright light, you might need to start with screening and acclimate them slowly. Some corals just don't do well with very bright light, though.

[pitogo]

I have 2x175MH 10K at 12 inches above the waters surface. I did that because I think it should decrease the heat transfer to the tank and because I have a black center brace on my 37G (2 175 instead of a single 400). Should I move it down to 8 inches?

The hood is 18" tall with about 1.5" space above the reflector and it vents through a 2.5" slot in the rear. On the sides are 2 120mm fans blowing into the hood forcing the heat up through slots in the reflector and out the black slot. I'm getting good growth, all my rocks are turning purple and green. I'm sure its green coralline algae (growing in circles like the purple stuff).

Anyway, 4 inches is a lot to lower it and at 3" above the water, I could barely look at the tank my eyeballz were burning from all the light so I think 7-8" is good. The only other change besides the height is to change from 10k to 14/15K next round. Its a small tank and its costing me about $22-25 month to run it.

[ron100m]

Thanks, I previously had two separate hoods with 20k bulbs and it got old and changed to new fixture and also changed to 10K with PC's in the blue range. But when I changed it out about 6 months ago things started going South with corals/algae /red slime. PH, KH,PO4, Ca everything else stable so I was trying to find the cause. I probably had them a little close, about six, I backed them to 12 because it is running a little hot and keeping the chiller on all day.
Thanks, I'm sure I'll have more problems, like my button polyps that closed after being open for 11 years and surviving all kinds of trouble. Been closed for two months but not dying.

[gonzalezcp]

some height is preferable due to heat transfer.. I use a enclosed light assembly with fan plus a 8" vented canopy that the light assembly sits on top of. The lights can add a significant amount of heat if they are too low or and/or not vented.

[coralmkr]

8"-10"