Brandie, Do you have only one 250 watt mh over the 90 gal ? If so, place sun loving corals under the mh and non loving towards the sides. The radium 20k gives a nice crisp white w/hint of blue. A 6,500 bulb (such as Iwasaki) will be more yellow, but give more growth. It all depends what you like. LED strips will replace those CF bulbs in your fixture and give you much nicer color IMO.