How high can free chlorine levels be before they attack CV-600/700 enzymes?
In our field experience, we have increased free chlorine up to 20 ppm (while cleaning up a green pool), and our CV-600/700 enzymes performed well. We have not tested higher levels, but to be safe, Orenda enzymes can perform fine up to 20 ppm of free chlorine. And we see no reason for a swimming pool to have chlorine levels that exceed 20 ppm.
We cannot speak for other brands of enzymes. We can only speak for our own enzyme products, CV-600 and CV-700.
Chlorine is usually the primary sanitizer and oxidizer in water
Unless your pool is using a chlorine alternative sanitizer, chlorine will be in the water as your primary sanitizer and oxidizer. It will oxidize just about anything, and theoretically, it can oxidize enzymes. However, our enzymes are resilient and cohabitate well in normally-chlorinated water.
Do not mix enzymes and chlorine directly together because in such high concentrations, there may be an adverse reaction. Only use these products as directed in a swimming pool or other water system. When adding high levels of either chlorine or enzymes (or both), start with chlorine, then add enzymes afterward in a different area of the pool (or directly into the skimmer or gutter). This allows for the products to dilute and spread out so they are not as concentrated when they interact.