Anyone run a MH 4" above the water line?

[aquageek1]

I just bought a beautiful new stand and canopy for my 90g. I thought the canopy would be adequate because the top of it sits 8.5" above the top of the tank. However, DUH DUH DUH , when I went to attach my MH reflector, I realized the placement of the mogul base sits about 4" below the reflector, which would place my bulb about 4.5" above the waterline. I have a glass top I could put over the tank to act as a barrier, but I'm afraid it will heat the tank too much and really don't want to run a chiller. Is it feasable to safely run this bulb that close (4.5") to the water? Any opinions or experiences with this? It's a 250wMH. Thanks.
Pete

 

[Len]

I've done it with 175W, but it's risky business. Any splash on the bulb will cause it to explode. Heat will be an issue. You can use more fans in the hood to help out, but come summer, you may have temperature issues. Another concern is that 4" will give the bulb very poor distribution. Reflectors are usually designed for 6-12" height above the tank.

Depending on the 250W ballast, you may want to consider switching to double ended, which you can mount more flush to the canopy's top. I'd still leave 1/2" to 1" of spacing between the reflector and the wood to allow for proper heat disappation, but with a DE bulb, the bulb will at least be 5-7" above the water. You'll need a glass shield to both protect the bulb from water and to help filter out UV.

 

[aquageek1]

What if I use the glass canopy, but raise it so it sits a couple of inches off the top of thank? Would that allow for protection of the MH bulb against water splash and allow for better cooling of the water?

 

[Len]

If you can get the bulb about 6" above the water, you're in pretty good shape. Anything less then four and I'd be concerned. The glass will help protect the MH against splash damage, but realize it will also cut down a lot (upwards of 30%) of the output, not to mention shift the spectrum.

 

[FragMaster]

I have been running a 175w 12k for the past 3 years over my 29g reef at 5 inches off the water line. Its been spalshed, and salt creeped to heck and back.
I think it depends on the quality of the bulb as to how easly it will explode.
Now HPS bulbs will explode VERY fast that way.
Thinner glass wall.

 

[aquageek1]

I think it depends on the quality of the bulb as to how easly it will explode.

I have an Aqualine Bushke, good quality I believe.

I think I may try it without the glass and see what happens. If I need to raise it, I'll rig something. The back of the canopy is open so I'll some fans to push out the heat - maybe run a fan blowing in on one side of the back and the two blowing out on the other side to create kind of a grade to the air movement.