My American cart. filter has a broken o-ring which I cant replace as it is obsolete. Im looking to replace with either sand or DE. Have a 22K IG pool with a 1.5 HP single-speed pump, 1.5" plumping, ~ 90-100 gpm. Pump is ~10 yrs old. Would be nice to replace with a new energy efficient model. How large a sand filter do you all think I would need with the existing pump? Any suggestions for a new filter/pump combo?