To say "confused" is an understatement. Reading a ton of messages pertaining to this subject, as well as trying to correlate the answers with my own experiences over the past 20 years, I arrived at an impasse.
The information at the Chemical forum seem to augment my suspicion, that the high CYA reading is the cause of my current dilemma, which is further corroborated by the opinion of my pool supply company.
The current problem, manifested itself within one week, even though I believe the cause dates back to last season, when I was unable to maintain a chlorine level above 2 to 4 ppm, running the chlorinator fully open at 8, when previously a setting of 3 sufficed.
Starting out I had a free chlorine reading of 2, PH of 7.0, Alkalinity of 80.
Added ca. 2k gallons of water, and shocked the pool with 3 bags of Leslie's Power Powder Plus.
Took another reading a couple of days later, since normally it takes about that long for the excess chlorine to dissipate. (FC 1, PH 7.2, Alkalinity 90)
Three days later it rained (6 to 8 inches) rain and the water got a tad cloudy.
Shocked again with 4 bags of Power Powder Plus. (Recommended shock treatment is 1 bag per 16,000 gallons).
Within 3 days, the water turned green and today it could be mistaken for a Louisiana swamp.
Took a water sample to my Pool Company and had them test for cyanuric acid. Their test showed about 150 ppm, and your chart indicates that the free chlorine has to exceed 39 ppm at 100 ppm stabilizer.
Here lies my confusion. One post on your site claims that the cyanuric acid diminished over the winter months, which mine obviously did not do, other information found indicates that CYA accumulates and the only way to reduce it is by draining some of the water.
I think, by writing this post I may have answered my own question, but would appreciate a little clarification.
Super chlorination (>10ppm free chlorine) will kill algae?
Why then does high CYA require 39 ppm chlorine for shock treatment
Please pardon this lengthy post. I hope that someone has the patience to read through it and help me with this quandary.