Can you visibly see the bubbles in the sump? Might just need to find the source and see if you can isolate it from the pump. Turn the skimmer off for a day and see if you see a difference.
I have a ton of bubbles that come from my drain but the distance from the that an the pump is enough for the bubble to subside. I try to make my skimmer dump by the drain so it dissipates as well before getting to the pump.
experiment and see what happens.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,