Hey all. I started doing the TFP method back in November. Prior, the pool was maintained weekly by a service. Trichlor pucks were used then and when I started, the CYA was well over 100. Via Taylor kit and 1/2 dilution, the best I could estimate was130-150. Since I was not going to use the pool for the winter season, nor heat it, I decided to forgo a major drain and refill. I drained down a little bit a couple times due to rainfall fill but not much.
When I started up the pool in March, I found that my CYA was about 80 - 90. Didn't need dilution but after doing the test a few times you can see how cloudy. So I decided to leave it there and keep my FC around 8-9 which required about 1-2 pints of 10% each day once the pool temp got to 86 degrees. The pool doesn't get heavy use - just my wife and I each day for an hour or two.
I decided to check CYA again and saw it was around 40-50! I ordered the standard and verified. Even without that, I could see it was much less cloudy than in March. I only drained about 2 inches of water off the pool once due to rain and in the spring had to add some water. But I always read that CYA won't evaporate out. But it obviously does go down. We don't have splash out.
Anyway I found it interesting and thought I'd share. I'm glad I know I am able to get a somewhat reliable CYA reading.
My latest pool numbers:
FC - 6.2
CC - 0
TA - 70
PH - 7.6
CH - 310
Borates - 30-40
CYA - 45