I agree only buy Iwaski 6.5k or german= AB or ushio or equals like halmiton ect... no blueline no sunbust no Chinese bulbs. USA,Japanese,German =good. IMO 250w would be fine. I've seen small tanks with 400w they need to keep the bulb higher. IME very few ppl accually have sps that likes to be 7" away from the bulb. Sure they can aclimate sps pulples ect to like them but 250w I've seen sps in small tanks do fine.What the furthest away would still be under 20-24".? Max on the bottom? From the bulb. If you use dsb @4" keep bulb 6-8" away hmmm most distance would be 26" away from the bottom. Most sps will be @10" away? Nice color you should have IME. 400w may give alittle mosre color and faster growth but 250w with a good bulb will make them frags growplenty fast. I use 250 6.5k and have a birdnest that grow 1/2" less than a month= just got it. Montipora that grow 1/2=1" a month. But have some slow growers that only grow @1/8-1/4. = 400w probally would help there. But heat and power was a concern at the time. When setting up my tank.