When my new pool was first opened this summer, and before I knew anything about this forum or the BBB method, I was using dichlor granules and trichlor pucks. So obviously by the time I bought my TF100 test kit and measured my CYA level, it was no surprise to find it at 50. But now I'm using the BBB method and have introduced no CYA (that I know of) into my water and yet the CYA level is increasing slightly. A few weeks ago CYA rose to 60 (I realize with the inaccuracy of the test - and my interpretation of it!! - an error margin of +/- 10 isn't inconceivable, so I didn't think too much of the increase to 60). But yesterday I measured again and now my CYA has risen to 70.
I realize none of these numbers are catastrophic, and it just means I need to increase my bleach a bit. But I'm still curious as to where the extra CYA could be coming from.
The only other things I've been putting into the pool are:
Algaecide - 1/2 qt every other week (only because startup company gave me the stuff and instructed me to, so I'm using it up)
Les-iron - Only used this for the first few weeks and haven't added any since about 3-4 weeks ago.
PoolPerfect - Just started using this 2 weeks ago to help breakdown the excess tanning oils, etc.
Would any of these cause the CYA increase?
Any other explanations?