MH Lights, placement and timing

J

johngp

AC Members
Sep 20, 2004
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Swindon UK
www.wild-africa.com
I have a 120 gallon tank being set up for mini reef, I have 2x250 MH units (1400k bulbs). the tank is 2ft deep. I dont intend to have a cover on the main tank (I appreciate that I will get evaporation and Im installing an RO unit and level monitor). How high off the water level should I mount these lights for maximum value to the corals and do I need further lighting (actinics or moon ?) to further help.

I also read somewhere that you overlap each of the main lights on and off times so that it simulates the suns movements!! - seems a bit OTT to me though - any views ? ;)
 
I'd mount them at least 9", up to about 12" from the water surface, to keep them from heating the water too much. If you aren't using a canopy, then heat will be less of a problem.

I don't use a glass lid either, just another thing to clean. You will be so happy to have an auto-topoff system. One less daily chore to do.

If you get halides with the right spectral output (color tempertaure is not the whole story), you don't actually need actinics. There are several reasons to use them, though. First, a little extra light at the blue end probably helps growth. Second, it makes the tank look nicer to many people's eyes. Third, I only want to run my halides 8 hours a day, but want to see my fish and corals longer than that. So my actinics are on at dawn and dusk, with the halides coming on mid-day.

Moonlights are probably fine, but I don't think they add anything for the inhabitants. If you have ever been diving on a reef at night, you'll know that it's darker than your living room in the middle of the night. If you want to watch things on the sneak, I'd suggest going to Radio Shack and getting a red LED, which a lot of inverts can't see.

With two lights, I don't think any of your critters would be fooled if you tried to simulate the sun's motion.
 
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