Adding CYA Caused Other Water Chemistry Issues

We have a 9,000 gallon wading pool and we use the AK110 Pentair Water Chemistry Controller to inject chlorine and muriatic acid. Recently we started using cyanuric acid to reduce our chlorine use, but it has caused the other water chemistry to be off. If left to its own devices, the controller will inject way to much chlorine, sometimes too much acid, and the ORP is still dropping below 700. Now, even when the CYA levels are barely detectable (<30) the Controller still injects too much chlorine. There were several mornings we came in and the chlorine was well above 10 so we had to dump and add water before the pool could open. Could the CYA have damaged the sensors? Do we need to reprogram the Controller now that we are using cyanuric acid? We have compensated by turning the chlorine/acid injectors off once the chlorine/acid levels are good and then turn it on once or twice a day as more chlorine/acid is needed. By doing this our ORP is too low. Does anyone have any suggestions for why adding CYA has caused these issues or how to trouble shoot this? Thanks.

Wow! Your fundamental assumptions about CYA and chlorine are all upside down and backwards.
CYA protects chlorine from rapid breakdown by slowing down its action. Therefore, the more CYA you have the more chlorine you need to maintain sanitary water. We recommend a minimum of 30 ppm but a high of no more than 80, and that is for particular circumstances, like a salt water chlorine generator or you live in a hot humid enviroment and cannot control chlorine usage.

You need to look at our Best Guess table to see the relationship.

http://www.poolsolutions.com/gd/best...ine-chart.html

You can safely swim in water with a chlorine level of ten. If your CYA is 30 ALL you need to worry about is your bathing suit fading...so wear an old suit. If your CYA is 80, you don't even have to worry about that!

This is just for starters...