Diagnose and correct over-stabilized (high cyanuric acid) pool water

Steps

1. Test CYA with a turbidity (View-Through) test or a dedicated CYA reagent kit, since standard DPD chlorine tests do not measure CYA.
2. Compare the result against the operating ceiling actually adopted by the local health code; the CDC Model Aquatic Health Code (MAHC), 5th edition (December 2024), sets a standard operating limit of ≤100 ppm and flags ≥300 ppm as requiring immediate remediation — but confirm which MAHC edition (if any) your jurisdiction has adopted, since older editions used a lower ceiling.
3. If CYA is elevated, calculate the dilution needed: fraction of pool volume to drain and refill with CYA-free water ≈ 1 − (target CYA ÷ current CYA).
4. Drain and refill in stages, retesting CYA after each partial drain-and-refill cycle rather than assuming the calculated fraction lands exactly on target.
5. Switch future chlorine feed to an unstabilized source (liquid sodium hypochlorite or cal-hypo) to stop adding more CYA while the level is corrected.