I'm assuming you are gravity feeding from fish tanks to your 55 gallon filter, and then pumping water back with that single external pump. If so, it's often called a "CHOP" system (Constant Height, One Pump). It's a nice and relatively simple to use and maintain RAS design. Now you need to add an RBC for additional bio filtration! Really helps keep things stabilized.

Good luck with the Tilapia!

12 ac pond in NW Missouri. 28' max depth at full pool. Fish Present: LMB, BG, RES, YP, CC, WB, HSB, WE, BCP, WCP, GSH.