I’ve been battling this issue for the past 2 seasons. This is what I have in a nutshell. Vinyl inground pool about 30k gallons with a gas heater (which my wife loves to run all the time). With that being said. Once the pool is open I will have to back flush the DE filter just about every 2 weeks because the operating pressure will go from about 19 psi to 30 psi. I tried some new things last year, but it didn‘t seem to help. 1. I switched from Sam‘a chlorine tablets to Biogaurd 3 in 1 tablets