I have a new pool build. 21,000 gal. 2.75 HP Hayward variable speed pump with Hayward 4 cartridge filter and salt generator. Not long after my pump switches from 85% to 50%, a small bubble forms at the top of the reservoir. The longer it stays at 50% the bubble becomes larger and larger until eventually the water level in the reservoir drops 1-2 inches from where it was completely filled with no evidence of air at 85% . This happens every time. We also get air bubbles in one of the returns at 50% however this may be related to the salt cell generator. The pool builder claims it is “normal“. I’ve had a pool service company come out as well as a leak detection company who all agree that is not normal, but cannot find a cause. Hayward says it is also not normal but is likely a plumbing issue such as an obstruction or too many 90s etc. vs an equipment issue. We have lubricated the O-rings, cleaned the filters, and tightened all the joints. I don’t feel this is normal and am not sure what the next steps should be. Any insight is appreciated. Video attached
Pump Cavitation
- Thread starter magpie005
- Start date
Not saying that this is what’s causing your situation, a customer from 4 years ago contacted me last week and advised that this was just found in their pump basket. It’s probably 4-5 inches long and took up maybe 1/3 of the pipe, that’s a long time to make its way to the pump restricting flow the entire time.
- Jun 22, 2014
- 48,011
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Welcome to TFP! 
I agree that it could be a flow restriction. It could be something as simple as what A~H posted above stuck in your suction line. It doesn't take much. You could try pushing water backwards to see if that helps dislodge anything. In comparison, it could be a restriction after the pump preventing water from flowing efficiently back to the return jets. I have a similar issue, and the dirtier my filter gets, the faster (and lower) my pump pot water level gets. The filter may not look dirty, so water testing with a TF-Series (or Taylor K-2006C) test kit is a MUST. Clear/heavy organics can overwhelm a filter in a matter of hours and you'll never know it by looking at the water. So be sure you are testing your own water with one of those tests kits I mentioned above.
One thing your builder and others failed to mention to you in your original post was that VSPs do tend to see more air in the pot over the course of the day, especially at lower rpms. That indeed "IS" normal for many VSP owners. We see it here all the time. Many VSP owners simply program their pump to kick up rpms once or twice a day to purge that air. So before you get too worried, make sure there are no post-pump restrictions like a dirty filter (test properly!), and purge the pot once or twice a day. As long as you don't see a huge drop or loose prime you should be okay.
So yes, "ideally" the pot should stay full, and when it doesn't, in "many" cases it's usually a suction side leak pulling-in air. It could be anywhere from the skimmer(s) to the pump pot itself, including the pump lid an drain plugs. But it's a new pool, you've had a leak detection company check, and you mentioned all O-rings are lubed, so that would appear to rule that out. Also ensure your skimmer weir door isn't getting stuck somehow. If all of that is good, I would (for now) focus on proper water testing and scheduling a pot purge once or twice a day then monitor. No need to drive yourself nuts just yet.
I agree that it could be a flow restriction. It could be something as simple as what A~H posted above stuck in your suction line. It doesn't take much. You could try pushing water backwards to see if that helps dislodge anything. In comparison, it could be a restriction after the pump preventing water from flowing efficiently back to the return jets. I have a similar issue, and the dirtier my filter gets, the faster (and lower) my pump pot water level gets. The filter may not look dirty, so water testing with a TF-Series (or Taylor K-2006C) test kit is a MUST. Clear/heavy organics can overwhelm a filter in a matter of hours and you'll never know it by looking at the water. So be sure you are testing your own water with one of those tests kits I mentioned above.One thing your builder and others failed to mention to you in your original post was that VSPs do tend to see more air in the pot over the course of the day, especially at lower rpms. That indeed "IS" normal for many VSP owners. We see it here all the time. Many VSP owners simply program their pump to kick up rpms once or twice a day to purge that air. So before you get too worried, make sure there are no post-pump restrictions like a dirty filter (test properly!), and purge the pot once or twice a day. As long as you don't see a huge drop or loose prime you should be okay.
So yes, "ideally" the pot should stay full, and when it doesn't, in "many" cases it's usually a suction side leak pulling-in air. It could be anywhere from the skimmer(s) to the pump pot itself, including the pump lid an drain plugs. But it's a new pool, you've had a leak detection company check, and you mentioned all O-rings are lubed, so that would appear to rule that out. Also ensure your skimmer weir door isn't getting stuck somehow. If all of that is good, I would (for now) focus on proper water testing and scheduling a pot purge once or twice a day then monitor. No need to drive yourself nuts just yet.
Just remember that when air leaks are ruled out, it can only be two more things, suction side or pressure side has a restriction of some sort. Are you certain you don’t have a compromised pipe on the suction side?