I got a Pro-Clear Aquatics RedFlex 400 Sump for this system. After some research I decided to retrofit the filter sock areas with the Klir roller-mat filters for two of the slots and then I plan to plug the third hole (it comes with three, 4" filter socks. The only modification I had to do was to Dremel the area above the filter socks to accomidate the rectangular shape of the Klir filters. I also had to plug the wave shaped slots that allow water to exit the top of the filter sock chamber. This was necessary because the Klir need to the ability for 1.5" of water above the holes for the filter socks in order for the optical sensors to work properly. I used flextape for starters. I may eventually glue pvcboard over these slots if I want a more permanent solution. I also increased the built-in intakes from above. The Redflex came with 1" bulkheads, I went up to 1 1/2" to match my main overflow.