I agree w/Joshua - too much flow. Didn't see the size of the sump above, but that obviously factors in. In general, 5x or less of your tank volume is a good target to push through your returns - so that's probably 800 - 1000gph depending on your tank's actual water volume.

The sump is where most of the gas exchange occurs, and the longer the water is in the sump, the more your skimmer can work on it.

Sounds like you have several other pumps in/out of the sump for the skimmer, canister filters, etc. If the in/out for these are from different chambers (across baffles/dams) then you will be increasing the flow across the baffles. This can result in more turbulence in the sump and trap microbubbles that will get returned to the tank :angry

I have a 700g capacity system (probably 500g operational) with a 160g sump (probably 100g working volume) and I have a nice calm 1500gph flowing through the sump. In/out to other equipment (such as the skimmer) are as early as possible in the flow direction ("dirtier" water), and as far as possible from the return pump - time for bubbles to escape to the surface.

This is one of the design details that most folks don't spend much time on - bulkeads, pumps, etc. are connected where they fit or where it is easiest. Take some time designing our "filtration system" - it IS the most important aspect of a successful tank!