Light height

bucksfan1976 · Jul 22, 2013

I have a question, I have a 30 inch halide/t5 light on my 93 cube. With the legs the fixture only sits about 4 inches off the tank. Due to this I dont think Im getting a good spread on the halide, its more of a spotlight. How high off the tank should the light be. I was thinking of using some 2x4s and building a higher rim to raise the fixture up a couple of inches.

Genesis Corals · Jul 22, 2013

Find someone with a PAR meter and experiment with some different heights. There is no set height for lighting, depends on your tank and the intensity/spread you want.

Reefing Madness · Jul 22, 2013

Mine are only roughly 8" off the water.

Ron Reefman · Jul 23, 2013

There is no standard because there are WAY too many variables to consider, tank dimensions, MH bulb make and number, fixture reflector, height off the water, depth of the tank... The question is, you say it looks like a spot light, so raise it up until it doesn't. It may well be that 1 250w MH isn't enough for your tank. I have no idea how long your 93g cube is. I had 4 250w MH over my 6' long 180g tank and I had no spotlight issues. Sounds like maybe you need a 2 bulb fixture?

jservedio · Jul 23, 2013

Just keep raising it until you don't get the spotlight effect - probably 8-12" off the surface. If you have a standard 30" cube, that probably isn't going to be enough light if you want to keep SPS anywhere but directly under the MH.

They make nice hanging kits so you can hang the light from the ceiling and adjust the light up or down with basically the press of a button - shouldn't run you more than $20 or $30 and almost all fixtures have a place to mount the hanging kit to (filled in with screws).

The nice thing about moving the MH up is you will dump way less heat into your tank. A lot of the heat will dissipate once the fixture is 6-8" above the surface of the water and if you use a fan, you will get almost no heat transfer.