I've been noticing that I get small amounts of air bubbles from my Polaris (pressure side) return. I cannot see any visible bubbles from either of my other 3 returns. the bubble are there even when the Polaris booster pump is not turned on. I've attached a picture of my setup. You can see that there is a dedicated return line from the Polaris booster pump. The booster pump sucks the water from the main return (which goes to all 3 pool returns). I know that return line bubbles usually mean some air getting in on the suction side, but if that were the case, then wouldn't I see the bubbles at all the returns?
My first hunch is to check the suction side connection of the booster. Both at the booster connection and where it connects to the main pool return line. But there are no visible leaks at either connection and I know if I take it apart, it might make things worse