so one of those 175 watt metal halide will work for my 3 foot long and 1 1/2 feet depp 40 gallon, i must know cuz i dont want to wate any money. i must know for sure. SO im not gonna need any antic PC's or anyoter lighting this will be fine right?
I think the rule of thumb is that it will light a 2x2 foot square. I am sure that you can place clams directly under it and do fine. The ends of your tank may be dim and the actinic supplementation is mostly for aesthetic purposes. Color is up to your own personal preferences. But a clam can live under a 175W MH. Keep in mind there are more critical variables than just lighting to keep clams happy.