I've had this pool for 15 years, but this is the first year that I've been closely monitoring the chemistry (just spent 3500 on a new heater). CYA has been steadily inching up to 120. After downloading the Pool Calculator and plugging in today's readings, I realized that with CYA at 120, the amount of FCL required to properly sanitize the water goes up to the 9-15 range. I had been maintaining it between 3 and 5. Am I understanding this correctly?