I have the same problem. I have a submerged 500 gph
pump in my sump with a sponge on it, and there are always tiny tiny tiny little bubbles comming from the power head. I also have a foam sponge on the overflow intake, and again after the water makes it through the sump.
As water spills into the surface skimmer, it makes bubbles, but these bubbles are stopped by the sponge on the other side.
Then the water travels down what looks like a vaccum cleaner hose into the sump. Where the water comes out there, there is also a TON of bubbles cuz that is where the protien skimmer is.
This water overflows to the bio-ball region and then through another sponge before entering the area where the return pump is. The return pump has a sponge on it, too.
And I still get tons of tiny bubbles coming out of the PH
I really would be interested to see how to make this go away.