Frag Tank Ideas?

[flyingarmy]

I am looking at adding a frag tank to my current 20 GAL Reef, not only to grow frags but to increase the water volume. Anyone already doing something like this? I am looking for ideas/solutions. Space is limited and I can't put it underneath, already running a 15 GAL sump/refugium. I was thinking of a additional tank beside my 20GAL Reef, a little lower with an over flow and return pump. Trying to grow frags in you display tank, esp one this size, is just not feasible. Thanks for the help in advance!