personally I just pulled my 175's out of my 150 gallon and added 400's. With that being said, the 400 watt ballast and sockets were given to me and I added them knowing the risk of bleaching and a hot tank. If it weren't for my tank being 25 inches deep, I would have never pulled the 175's. I like the iwasaki 15K bulb. From what I could find, there are only 12 or 13 250 watt bulbs on the market that throw out more par. They are pretty white though so actinic is a good thing.