I have a 120 gallon 48x24x24 with 2 400 watt MH and 2 110 watt uri actinics. I was usuing 6500k Iwasaki's but switched to 10000k Ushio last a few days ago. I like the color a whole lot better but It has not been long enough to tell anything about the growth rate. I don't plan on fragging it...