25,000 gal pool with SWG. During the winter I turn off the SWG and add a few pucks a month to the water via a floating dispenser. I have not added CYA to the pool over the last four years.
I add about 1/2 gallon of acid a week to keep proper pH.
In the summer, about every 7-10 days I add 3 bags of "sodium dichloro-s-triazinetrione" powder. (Yes I know you guys discourage powder shock, but it does work). I also add some phosphate lowering product (I know you hate that too) in the spring. Finally, I do add a small amount of bromine ("No-More problems") every few months. All of this will usually keep yellow algae out of my pool.
So this week I tested the CYA level and it is greater than 100 !!! Tested it again, made sure it was mixed properly and got the same results. I am using the Taylor test kit where you add the mixture (7 ml pool water+7 ml of reagent) until you cannot see the black dot anymore.
What is happening???