We have a 30,000 gal in ground pool with a 1 hp hayward super pump and a sand filter.
Drawing only from the 2 skimmers we get no air visible in the pump housing during operation, but when we open the main drain inlet to the pump, we get a flood of air bubbles - really a torrent.
1. I know it seems obvious that there may be a break or a crack in the main drain line between the bottom of the pool and that diverter valve just before the pump intake, but is there any other possible explanation? There are no known water leaks or unexplained water loss.
2. If you can keep the pool clean just drawing from the skimmer baskets, do you really need to open the main drain during normal operation?
Thanks for any expert tips!