Here's the details on this pool. 1988 16x32x8 vinyl in-ground pool with Super Pump, S-200 sand filter, new VariFlow valve as the old one was leaking and beyond repair. After 25 years of use, the system is suddenly spewing silt from the return port when vacuuming and silt is building up on the bottom of the pool. Never had this issue before. I took the filter top off and skimmed the filth (greasy sun block) off of the top of the sand and replaced that with some new sand. Still getting silt out of the return port. At the advice of two pool shops, I vacuumed to waste, but still have silt on the bottom after running the system all day. Not losing any water level with the new VariFlow valve in place. System pressure has stayed at about 14 - 15 psi and hasn't risen to 25 psi for about four weeks now when the silt started appearing. With the pump running, it will spew bubbles out of the return port every 15 to 20 seconds. No bubbles in the riser pipe from the pump into the VariFlow valve. Also, no sand in the sight glass when back washing. I have some questions.
1. Should I do a deep clean of the filter as described in the sticky section here?
2. Should I remove the sand, clean it, and check for some internal structural problem?
3. We had a really harsh winter here with the freeze line extending down to 4 feet. Should I get someone out to check the runs for leaks? Thought is one of the suction lines is pulling in some dirt. Never had an issue with them before, only some corroded clamps on the skimmer.