Protein skimmer overflowing
Is it possible that you have it sitting in to much water in the sump? Keep in mind that skimmers have recommended water depths to sit in and it the depth is to high you will run to wet of skim. I had a similar issue with mine, spec is 8-10 inches of water. I had it running in about 10 inches and it was good, lowered it to 8 and it ran really wet, raised it to 9 and no issues again. Something to consider as the water depth the skimmer sits in directly effects the water level in the skimmer. You can try using a piece of eggcrate to raise it, that will give you 1/2" per layer. Run it for a few days and see if that helps, if not add another layer. FYI eggcrate is also known as lighting diffuser found in any hardware store, 24"x48" sheet and it's 1/2" squares.
Sorry I have that backwards, was in 8 then lowered it to 10 then raised it to 9.