I have two tanks, basement sump and fuge total 350 gallon system with a 1/4 H.P. chiller and it works as long as I A/C the house to 78 deg. Course the basement sump is a huge help here. Oh yea, I have two 250 watt MH 12, 39 watt t-5 ho, 2 65 watt pc. for lights.
If I were to buy for this setup and not upgrade like I have to here, I would buy a 1/3 H.P. though.