In order to lower my salt and CH, I did a partial drain of my pool last weekend. I only drained about 15-20%. Before the drain, my CH was at 1100 (!) It was 44 drops with a 10ml sample. I assumed it was this high because I know the water in this area is rather hard. But when I tested the fill water, it was only 40. The pool is about 2.5 years old with the original fill water. Is there a logical explanation as to how the CH got so high? I never tested the CH because the store told me I didn't need to and then I found this site, so I don't know what the CH was for the first 18 months.