What is CYA?

I see the term CYA used a lot. What is it, and why is it so important?

Cyanuric Acid. Also known as stabilizer. A vague and general answer to why it's important is that it protects chlorine from the effects of the sun, and it restricts the ability of chlorine to sanitize in at least some ways. Striking a balance between the two is the key.

To add to what JohnT said, CYA also controls as to when the Chlorine is needed. However, too strong a concentration, say 100 ppm, wiil prevent the chlorine from being fully utilized. Too low a concentration, say <20 ppm and the chlorine will evaporate before it can be used.

Ben, the moderator of this forum created a chart to help newbies and oldies to get an idea of how much CYA to add, based on the Chlorine level:

Stabilizer . . . . . . . .Min. FC . . . . .Max FC . . . . . 'Shock' FC
=> 0 ppm . . .. 1 ppm . . . . . 3 ppm . .. . . . .10 ppm
=> 10 - 20 ppm . . . . 2 ppm . . . . . 5 ppm . . . . . . 12 ppm
=> 30 - 50 ppm . . . . 3 ppm . . . . . 6 ppm . . . . . . 15 ppm
=> 60 - 90 ppm . . . . 5 ppm . . . . 10 ppm . . . . . . 20 ppm
=> 100 - 200 ppm . . .8 ppm . . . . 15 ppm . . . . . . 25 ppm

FC = Free Chlorine. This is the value that does the sanitizing so to speak.

Hope this gives an insight as to what CYA does.

Pat