5 watts per gallon but metal halide might heat up the water too much but 2 of those fixtures or 4 t-5s would be what you want. trust me, when you get addicted to this hobby your going to get that amount of light anyway so you might as well do it once and do it right. 5 watts per gallon and a good skimmer, don't skimp on those 2 things and you'll be good. good luck