Yeah I have three that run in mine. The ONLY problem (and it's not even an issue really) with the Koralias is that their flow is so widely dispersed, that even while pumping out 1200 gph, the flow is fairly moderate. I have a timer setup that runs the two corners during the day, and the center one turns on at night. I also have a mag5 as a return, which of course, is always on. In a 90g, I would basically do the same thing that I have done in mine. I have noticed that my tank seems to enjoy it more, also, I don't really have to worry about detritus building up anywhere, as I have powerhead washed my tank and nothing came out of the rocks. That being said, I do not have a whole lot of rocks in my display either, most of them reside in the fuge.
HTH!!!