dpd

We just opened our large 36,000 gallon pool. Pool opening test results were FC 0 pH 7.2 Total Alkalinity 80 CYA 0 Pool temperature 70 F I expected our CYA to be on the low side but not 0. It ran low all last summer and was 35 when we closed the pool in September. We have to drain...

What are things I need to look for if I'm getting pretty wide variations in FC when tested just a few minutes apart? I tested using DPD and got a FC of 4.5. I tested again, with a different sample bottle, in the same spot in the pool. I got 6.0. I figured "best two out of three" and tested...