My new tank is a 72" x 30" x 30" and I will be using 4 - 250w DE 12k RF. I wouldn't use 400w unless my tank was 32" I talked with Sanjay at Macna and he says that most people "over-kill" in the lighting department and that's why I'm staying with the 250w. He told me that they would be just fine.

S