This isn't an every day thing, and has only happened twice that I know of. I noticed once that my pump was running but I had little to no flow in the pool. When I looked at the pump, I noticed that the SWG had a big slug of air inside (casing is clear). I turned off the pump, turned it back on, and it cleared. Flow restored, although I still had a small pocket air at the top of the SWG. This happened one other time.
Yesterday, I had flow but noticed that the slug of air was large again. I turned off my polaris booster pump and the slug of air got smaller. Is it possible that when the booster pump is running (which is just before the SWG), that it is starving the main outlets of water? But how did the air get in there and how do I get it out? If it makes a difference- the outlet from the filter/polaris inlet is lower than the SWG and the SWG (which is inline) slopes up before hitting the discharge. I've thought about lowering the outlet side, making the SWG level before it 90s and goes to the pool, if this could be an issue.
Btw, haven't added a chemical to the pool in over 2 weeks, and it's crystal clear. Love having a SWG.