Manage cyanuric acid (CYA) levels relative to free chlorine, including when to drain/dilute the pool

domain: cdc.gov · 6 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗

Steps

  1. Test CYA regularly alongside free chlorine, since CYA is not consumed and only rises (from stabilized chlorine use or fill water) or falls via dilution/backwash
  2. Apply CDC's minimum free chlorine guidance: at least 1 ppm FC in pools without CYA, at least 2 ppm FC when CYA/stabilized chlorine is used, pH 7.0-7.8
  3. Treat CYA at or above 300 ppm as requiring immediate remediation, per the current (5th edition, released Dec 2024) CDC Model Aquatic Health Code threshold
  4. Reduce CYA by partially draining and refilling with fresh water — dilution is the only practical way to lower CYA, not chemical additives
  5. For any fecal/Crypto response, note CDC recommends getting CYA down to 15 ppm or less before relying on chlorine-only inactivation, since high CYA makes effective hyperchlorination impractical
  6. Switch to unstabilized chlorine sources (liquid/cal-hypo) going forward if CYA keeps trending up from routine dichlor/trichlor use

Known gotchas

Related routes

Diagnose and correct over-stabilized (high cyanuric acid) pool water
pool-water-chemistry · 5 steps · unrated

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