I’ve been dealing with bubbles in the pool return for over a year, as mentioned in this thread:
Polaris PB4SQ Suction Leak
I first followed the wisdom that bubbles are a suction-side problem and I set about replacing o-rings, tightening lids, watching soap bubbles, etc. All to no avail.
A buddy who used to do pool maintenance pointed out there’s no way that amount of bubbling was from a suction-side leak, because the filter pump would never have been able to pull a prime, which it did. So it had to be pressure-side.
Wouldn’t you know it, my Hayward puck chlorinator is essentially a Venturi injector. And digging into the lid yesterday, I see a kink in the o-ring, quite possibly letting the Venturi draw air. I straightened out the kink and carefully reinstalled the lid, et voila, the bubbles are gone.
I’ve got a new o-ring on order, and just wanted this out there for posterity, that bubbles in the returns CAN BE caused by a pressure-side leak.
(Now I have to figure out why fixing that leak caused my spa water level to draw down by something like 12 inches overnight, assuming they’re related.

)