JohnK, sounds like you have a neat setup, I think you might want a water exchange rate of at least 2 or 3 times an hour. My 100 gal tank for PS's uses a 300 gph pump to the biological filter and works great, they are fed heavily but the ammonia and nitrite levels are zero.
Here's a pump that might work well.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66514