Don't use the fuge as a sump...run it as a seperate tank, with slower flow that "feeds" fuge and over flows to the sump where it is pumped back to tank...
Slower flow can come from a line "Td" off the return line (portion of return flow) or a small pump to fuge
If fuge is below tank with sump...return fuge overflow to sump...
If fuge is above main tank...return fuge to tank...