I decided to build a refugium out of an old 50 gallon. My tank is a 40 gallon with a breeding pair of True Pecula. I would like to add a mandarin, so I will put my 50 gallon underneath with lots of live rock/sand. The refugium is about 3 1/2 feet below. How many gallons per hour am I looking at for a return pump? I bought a ball valve to control the power too.