I need to replace a sizeable portion of the water in our pool because of a high CH level (between 400 to 600, depending on whether I believe the pool store's reading or my own), and am wondering if setting the valve to backwash for an extended period of time (say 20 minutes or so?) is OK for our sand filter, or if I should just backwash it to waste? I'm thinking a long backwash might be good for the sand, but thought I'd best check here first.
