If you put 400W on a 28 Gallon tank you are either going to have to run so many fans that the noise will drive you nuts, or have to run a chiller. I had a 250W bulb over my 30G with two computer fans in the canopy and in the summer I fought to keep the temp under 84F. And the 400W puts out WAY more heat. I have two over my 150G that drains into a 75G sump in the basement. I know the canopy has almost no ventilation but I need a full size room fan over my sump to keep it under 81F. And that is in a basement! And last summer it went up higher, so I have to get a chiller myself this year.
Anyways, 400W is not necessary on such a small tank, you would be much better off with a nice 250W configuration, at the maximum. Plus there are so many bulbs to choose from in that wattage, in both double ended and single ended configurations.
JMO...
EDIT: I see you already bought the 400W. Now all you have to do is buy a chiller!
