Okay I am in the process of moving everything but my damsels to my new 20H, sorry but the damsels are going to the LFS. Anyway, my 5.5 is fully cycled and has been supporting the damsels without a problem. Once they are gone, I was wondering is there any reason I can't just use the tank as it sits (cycled and stable) for QT of my new fish when I get them?

Also can someone give me an idea of what kind of flow I will need (GPH wise) for my 20H ? I was thinking a 250 gph koralia and a 425 gph one. I'm planning on SPS high (and eventually a clam) and then zoos and mushrooms and some LPS lower and farther from the light (single HQI).

Thanks in advance guys.

A 5.5 is a perfect choice for a QT tank. You might want to remove the sand since it doesn't sound like a good idea for quarantining multiple livestock.

Those two koralias would be okay, but you may want to search for stronger powerheads, like maybe a vortech, if you want SPS.