I used three Dolphin Aquasea 4700 pumps for my tank. One for the return from the sump and the other two for two close loops (450 g tank) I had really good result with them. I used them for 5 years with only one problem and it was my fault. The seal in one of the pump leaks because I was adding sand to the tank near the intake of the close loop. The sand got suck into the close loop and ruin the seal. I have to send it back to Dolphin to get it replace. It is importank that you don't let the pump drag sand and shells into it's intake.
