Just opened the pool this weekend. 23,700 gallon above ground. Vinyl liner. Sand filter.
The CYA level was between 50 & 60 when I covered the pool last fall. I expected it to be about the same when I reopened. My test cylinder only reads to 30 and the dot on the bottom is still visible when the vial is full. My CYA level is likely closer to 20.
I didn't think this stuff went away. Reopening the pool required a <10% fresh water add. What could have caused the acid level to drop so dramatically over the winter?