MH over a 20 gallon...

[OCDP]

I use a 250w HQI Giesmann Nova II over my standard 20g tank. Things get a bit tricky when using this much light over such a small tank. I have used everything from 2x65w PC's to 150w HQI to the Aqualight Pro, and settled on 250w HQI. Why? Because this way when I upgrade I will have the proper light I need/want. Secondly, I just like to have lots of light... your corals will thank you, the growth is awesome and I just like the look of a bright lit up tank.

Obviously with this intensity you face other problems ... evap, temp swings, burning corals, etc.. but it's not so bad. Summer time is my biggest problem... it's really hard to keep temps under control, so I usually add a fan to the mix, then face evaporation issues. In the end.. I'm happy with 250w HQI and so are my inverts (clams, anemones) and corals (I keep LPS, softies and SPS) . I'd say go with whatever you can afford.. if you can afford 250w ,go for it. You can always adjust the height of your light ,etc... then, if you do upgrade in the future.. you may already have the proper light for the system.

[canuckzilla]

So here's the next question for those having MH on a 20g tank. How high do you keep your lights from the top of your tank?

I have a 10k 150w and keep the lights 10-12 inches from the top. At 8 inches or lower, my coral was getting burnt near the top of the tank.