Split off of this topic because there are controversial subjects here that will be distracting in that topic. JasonLion
In addition to all the good advise above, please note that CYA tests, in our industry, are our least accurate.
Mainly due to the individual tester. the sample should be diluted 50/50 with distilled water. then carfully read
and the final result multiplied by 2.
also, what is your TDS reading? (Total Dissolved Solids)
Higher TDS levels can cause more problems than high CYA.
if you are still fighting this problem - this has worked well for me in the past.
1. treat the stain.
2. add the sequestering agent.
3. next day: double the chlorine pucks or load the feeder and set to high.
DO NOT SHOCK
stop using liquid chlorine, it doesnt help residential pools at all, it only adds to your
total dissolved solids, shortening the life of your pool water and making it more difficult
to effectivly sanitize the pool.
We all have good answers here, and ALL pools are different.
So try them and see which one works for your pool.