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
Test your CYA and see what it is at. If it is near 100 ppm try switching to liquid chlorine only for the season. You my need to add 4-5 gallon each week so the cost will be similar or higher than the tablets but the results will be that you are not adding CYA to the pool. Once the level drops to 30-50 ppm the liquid chlorine will be more effective and you will need to add less moving forward. It wouldn't be unusual for a 30K pool to require 1/2 to 1 gallon per day. If you had a Salt Water System it would be producing and adding about 1/2 gallon each day to keep the pool at 3-5 ppm.
The grids have a lifespan of 3-5 years. If the pressure is rising on you as you indicated replacing all 8 grids normally will solve this issue. Try that and see if it corrects it.