My pool is about 1 year old and I've developed a very odd leak. The system is drawing in air from somewhere when the pump is turned off. I believe it is on the outlet (pressure) side of the filter. When I shut down the pump a small, repetitive gurgle is heard. If I place my ear directly on the filter tank, a trickle of air rising into the filter tank is easily heard.
There are no obvious water leaks above ground at the pool equipment and no obvious soggy/boggy areas between the IG pool vessel and the equipment. After a few hours with the pump off, the filter tank is about 30% full of air (takes about 20-30 seconds to purge air out of the filter tank via the valve on top). However, the pump never loses prime and the pump pre-filter canister has no air bubbles in it. The pool is filled properly with no "vortex" in the skimmer while pump is running. I've cleaned all the o-rings thoroughly and re-lubed them to excess. No luck. Still have same problem. I've also closely monitored the plumbing while the pump starts and cannot detect any water being squirted out anywhere above ground.
Since the pool filter tank sits about 3 feet above the level of the pool, I believe the air is coming from somewhere below the filter tank. I do have a mazzei ozone injector on the filter outlet plumbing (red arrow in attached pic). I also have a Pool Frog system on the same return line (blue oval in attached pic). I can also hear a trickle of air flowing into this canister (similar to filter tank) after shutting down the pump.
Since the ozone injector is between–and below–the levels of the Frog canister and the filter tank, could this be the source of my leak.? Can these injectors fail and let air in after the pump is off? Since my equipment pad is slightly above the pool level, is it possible the water is draining back into the pool as it is being displaced by the air?
I'm stumped! Any help would be greatly appreciated.