This is my first summer with a pool and the TFP method has been wonderful - giving me a beautifully clear pool all summer. At the beginning of the summer, I had a high CYA level and had to replace water to bring it down to 40. I checked my CYA level for the first time in a little over a month today and it is below 30. I completely filled the tube and could still see the black dot. I am out of R-0013 reagent and just reordered a 16oz bottle, so I'll have to wait about a week or so before I can check it again.
First, I'm not real sure how this could have happened since the only way to lower CYA is to replace water. I do get a lot of rain in my area - could that explain it? It's also possible I simply messed up the test, but again I can't confirm it at the moment.
Second, should I even bother raising CYA? I've been maintaining my FC level at 5 ppm, but I only lose 1-2 ppm a day. I very rarely lose more than 2 ppm in a day. If that rate of decline stays the same, do you think it's even worth bothering raising CYA?
I do have some 1-inch trichlor tabs left over from the previous owner I can put in the skimmer basket, so it will be easy enough to raise the CYA.
Thanks for your help!
I thought I should add my full test results:
FC - 3.5 (just raised to 5)
CC - 0
PH - 7.8
TA - 70
CH - 120
CYA - <30
I may test CH again in the morning as well. Borjis's comment below helped me realize that if CYA has fallen I should expect to see CH fall too. This test would indicate it hadn't changed, but I had difficulty with that test today as the sample turned from a very faint red to a very faint blue. It was so faint I may have misinterpreted when it turned from red to clear to blue.