I'm so glad I found TFP! I just took ownership of the pool in my signature when we closed on our new house a week ago. I had been reading Pool School and the forums here for a few months before closing, and I think I have a pretty good grasp on the chemistry and what I need to do to maintain my pool following the TFPC method. I'm a little more shaky on the equipment though.
The previous owners had the wife maintaining the chemistry on the pool store's tests and putting in whatever they told her. She had an in-line chlorinator with tri-chlor tabs so of course when I tested the CYA it was 90 (recent pool store test had CYA at 45, btw). So I need to drain some water for a partial refill. The filter on the pool is old, but seems to be in very good condition. I doubt she ever changed the sand, and she said she rarely backwashed it since "the pressure never reads higher than 20," while pointing to an obviously non-functioning pressure gauge on top of the filter. My multiport valve has a "waste" setting in addition to backwash, rinse, etc. I understand I could drain the pool by setting the valve to waste, but would there be any benefit in doing an extended backwash to clean the filter media by essentially removing all the water I need to drain using the backwash setting? Would there be any harm in doing so?