24" high tank,I have them as close to the top as I can enough so they don't suck any air. Approx 3/4

I think the RW20's are overkill in anything shy of 7-8 feet long. I bought two for my new 7 footer. I placed just one to test it out in my 79" long 100 gallon and on the lowest setting it blew corals right off the rocks.

The higher up, the more "wave action" they produce. I usually have mine halfway down in a 24" tank. Mine is a LPS-heavy 165g (just under 6') and keeping them low gives me a nice wafting motion, as opposed to whipping the frogspawns and hammers heads right off.:wink:

I have 2 rx 8 on a 6 foot 135 gallon tank opposite sides and at full speed they blow all the sand all over.probably the rx15 would be more then enough for your tank.

I would also vote for 2 x RW 15s.

Thank you for all the input. Looks like it's going to be the 15s