What is the ideal cyanuric acid (CYA) level for an outdoor chlorine pool?

Keep CYA between 30 and 50 ppm. That range protects chlorine from UV rays without over-stabilizing it. In scorching climates, some pros push it to 60 or 70, but then you need higher free chlorine. Test monthly — CYA only drops when you drain or backwash, so don’t let it creep up.