Hello all; new to the forum after getting bum steers from the local pool store on why my Cl level wouldn't hold the past two months. After a different answer (and purchase) every time I went in, I learned on this forum that the reason I was having issues was my CYA level of 100 was not allowing my Cl (between 6 and 0, every two days) to work. 15 minutes on this site convinced me to skip the pool store and go to Bleach. I've given up on powdered shock, but still use the pucks, bleach, and acid (the psuedo-BBB).
To my point: I am perplexed by my TF-100 kit showing CYA at around 15 (hard to tell because 20 is the low limit), but the pool store told me it was 45 last week, and 60 today. TF-100 test seems pretty straight forward and has given me similar results twice (the only two times I've used it). Can I rely on the pool store for an accurate level? Is that test so subjective that it could vary by 30% in a week? They also told me that because plaster is porous, it can retain CYA, even after a water change and may "leech" back into the water. Sounds like baloney to me?
Thanks in advance for any insight.
12,700 gal IG plaster
CYA Somewhere between 15 and 60