I have an 18x32 inground pool with a PF-50 sand filter. I just opened my pool yesterday and started the pump and filter. It showed about 16 PSI on the filter to start with. Today, I checked it and it made its way to about 24 PSI so I decided to backwash. As soon as I started backwashing, the pressure dropped to 20 PSI but wouldn't go any lower. I let it backwash for a couple of minutes and the water was totally clear coming out of the hose. I rinsed to re-seat the sand and then went back to filtering. The gauge still shows 20 PSI. Why didn't it go down anymore than it did? It did this same thing last year and the only way I could remedy this was to replace the sand. I did that last year along with checking, cleaning and replacing the laterals, and it worked pretty normally for the rest of the year. Surely replacing the sand isn't going to be a yearly ritual for me. Is there some way to get the pressure to go down to normal levels? In years past, after backwashing, the PSI would be around 12 or 14. Is there something else that could be causing the pressure to stay so high? Any help would be appreciated.

Thanks,
Stacy