I don't want to get in to the argument either, especially since i'm just going by personal experience, and maybe I worded it wrong, but I've always had much better luck, happier corals, etc with MH vs T5. T5 imho is good to get the "look" you want from a viewing standpoint, but i feel MH is healthier for the corals. The parts of the spectrum that plants (in this case corals) need to flourish is contained in the MH. T5 adds the extra blues that WE like when viewing our tanks. If i turned off my ATI bulbs, other than losing PAR, i bet my corals would grow just as well under just the MH bulb. I'd just have to move some of them closer to the light due to the loss of PAR. If i had to choose one or the other, I would hands down have a tank with just one MH bulb like a Pheonix 14k, rather than a T5-only setup (which i've had before). Again, all just based on previous experience. YMMV.