metal halide?

[pomme]

how far away from the water surface should the lights be hung? i know it says a minimum of 20cm but is there a maximum and a optimum?

 

[Guest]

I would say most would stay within 8 or 9 inches from the water surface.... This will help keep the intensity towards the bottom of the tank as opposed to having them higher.. A MH light is recommended to only light a 2 foot by 2 foot square... So, if your tank is 24" deep, and you have a 6" sand bed, technically, the lights should be 6" off the water surface for maximum efficiancy. This of couse is a little close, thus the 8 to 9 inch standard...HTH...