Hmm... idk.. 21" is pretty tall.. I think if you would be able to get your hands on a nice 6x36 T5HO fixture you would be totally set.. but then again, like i said, 21" is pretty deep. However, i've read and heard that the cutoff for T5's is 24" so you may still be ok with the T5's. I know you don't like MH
's, but with 2x150w lights you would be fine to keep tons of coral, and with the 250w you would be able to keep anything you wanted.
I guess.. the only other solution if you didn't want to go MH
, and T5's just weren't cutting it for your tank and you didn't like your coral selection, would be LED
's. But those are generally more expensive then MH
's.. BUT they run very cool, and have a ton less power consumption than MH
Anyways... i still think you should do MH
's lol, but i think with a 6x36 T5HO fixture you would be ok.
Sorry.. but anywhere i said 6x36.. i meant 6x39. I think a fixture like this would be excellent if you wanted to keep softies, zoas, and some LPS
TEK LIGHT T-5, 36" Light Fixture 6 x 39W lamps by Sunlight Supply* - AquaCave
Just a little dreaming right here.. but if i had your tank.. i would buy this fixture.. assuming i had the money. God only knows what i could do with this lol
BELIZE SUN 36" HQI +T5 + LED Lighting System by Hamilton Technology* - AquaCave
Also.. this may not be the same for you, but i'm just saying... I also was not big on SPS
.. and didn't plan to have any.. but for some reason.. i feel myself wanting some of the REALLY nice Acroporas and the Montiporas.. and especially some of the Pocilloporidae. Green Birdsnest if my FAV.