I haven't been able to solve this problem. I'm getting lots of bubbles from the return, not a lot of suction, and the strainer box on the filter drops it's level suddenly, makes a whooshing sound, the hoses kick around and then it goes back to pumping ... albeit, with a lot of bubbles and low suction.
I had to replace the top on the filter strainer. I did this at night and put some teflon grease on the o-ring. A friend mentioned I could revisit that since I did it at night. I have, and it seems to be OK.
The hoses do not leak when I lift them to inspect, i.e., no water spray comes from the hoses.
I see no leaks anywhere on any connections.
I loosened and began to remove the head thinking the tank was full of air. Water immediately began to flood out of the tank so I figure it is full of water.
This is probably the third year on this sand.
It's a Hayward.
Anyone have any other ideas how air is getting in here? It does seem to be from the pump to the return, rather than before the pump ... but is that only because it's being pumped out and therefore visible as bubbles?