if you want to keep nothing but softies, then it will work...but IMO, zoas put out better color once acclimated to strong light, especially if you want the more exotic ones.
coralife are also on the lower end of spectrum for t5 fixtures. 2 bulbs wouldnt be anywhere near strong to enough to penetrate 21" of water and yet give u decent par even half way down.
how wide is your tank? you may want to choose another type of lighting like LED. check out par38 lights. they may a better option for you and will screw into a regular light socket. theyll penetrate pretty deep too using correct lenses. you have many options for these lights. nanotuners, ledio, ecoxotic are just some of the brands that carry these bulbs for reef purposes