You may want to look into VHO set ups as well as T-5. VHO lamps are longer and may provide more coverage for less $, I'm not sure. As far as color goes, w/ 20k MH lamps you should already be on the blue side. You could go w/ actinic fluorescents for some more "pop" from your corals and some fish, but the tank may be too blue. You can also do a dawn/dusk simulation w/ actinics. Something in the 10k range would add some more white to your current lighting, and 50/50's more whitish blue. It depends on whether you like a yellow, crisp white, or bluish look to your tank. Personally I would probably look at something in the 10-12 k range w/ 20 k MH. HTH