<a href=showthread.php?s=&postid=8187465#post8187465 target=_blank>Originally posted</a> by anjhof
I have a 75 now, with 2 250's over it. I also have 2 VHO's running on the tank. I have 10K XM's over the tank and it looks a little washed out. I have no heat issues with my tank now (running two 4" fans in the canopy though). The lights are also about 12" above the water line. This is something to consider in terms of heat too. I can't imagine running 2 400's over a 75g tank. I also think you could easily get some money for the extra 400's and buy some 250's. According to the calculator on RC, you will spend an extra $13 a month running 200 extra watts over the 250's.
I would rather have 2 smaller lights than one large one. If you put it high enough, it would probably work, but it seems like you are forcing it a little.