I have D.E Hayward 4820 filter, bought new grids (SuperPro brand) and put recommended DE amount in and my problem is the pressure keeps going up 20-25 psi. after being on for couple hrs, when running on filter mode. There’s no evidence of air leaks on the suction side. I checked everything possible and still can’t understand why pressure keeps going up. There’s no air building up in the top of the filter. Any help is appreciated thank you.