[ldzielak]

I think check valves are a mechanical items just waiting to fail. I agree that the head loss is substantial, but in my case w/ 4MDQX-SC is still to much flow, so I had to install a recirc line back to the left side of the sump.

Also a note if you are wet testing your setup like I did for 2 weeks in the garage. Fresh water and salt water do not have the same viscosity, so you can get a way with more flow when using salt water. I guess if it works with fresh water your on the safe side. My tank level droped 1/4" - 1/8" after the salt was in. My 2 overflows are not enough for 4MDQX, with the screens and the 90 at the top. I'm thinking of installing boxes on the towers. But I can still play with the restrictor on the recirc line.