From the Pool School:Where can I learn more about the concept of reserve FC as it relates to CYA? (A search brings up too many references to be useful.) Basically, I don't understand why FC has less effect at CYA 100 than it does at CYA 50. Links would be fine - thanks.Cyanuric acid, often called stabilizer or conditioner, both protects FC from sunlight and lowers the effective strength of the FC (by holding some of the FC in reserve). The higher your CYA level, the more FC you need to use to get the same effect.