High Pressure

[AD2404]

I didn't backwash this fall and subsequently ruined the de grids and blew the seal. I have new grids, manifold, and ring installed. Nautilus brand (Pentair 60). I fired up the pool and used pool first aid to kill any algae, then back washed to clear unwanted waste. I cannot figure out why my pressure is rising to 20-24lbs, without even adding the DE?
Any suggestions would be appreciate!

Thank you for accepting me,

Adam