250watt se halide on 20g?

[ReeferMush]

its not overkill I have never had any heat problems what so ever, and don't run a cooler. My light sits 4" above my 20 gallon and my corals are freakin' loving the amonut of light being shed above the tank(19 Watts per Gallon). Plus i've fragged one piece of Xenia and its doubling in size almost every second week , so just keep an eye on your water temperature/evaporation and phosphate levels because with that much light, algea growth is to be known to be a problem(if using normal tap water like i do)