Cyanuric Acid Dilution Calculator
Calculate how much water to drain and refill to reduce cyanuric acid (CYA / stabilizer) levels in your swimming pool to a safe target range.
Formula
The dilution formula for a single drain-and-refill cycle is:
Cfinal = C0 × (1 − D/V) + Cr × (D/V)
Solving for the drain volume D:
D = V × (C0 − Ctarget) / (C0 − Crefill)
- D = Volume of water to drain and replace (gallons)
- V = Total pool volume (gallons)
- C0 = Current CYA concentration (ppm)
- Ctarget = Desired CYA concentration (ppm)
- Crefill = CYA concentration in refill water (ppm)
This is a mass-balance dilution equation assuming perfect mixing and no CYA degradation during the process.
Assumptions & References
- CYA (cyanuric acid / isocyanuric acid) does not degrade significantly under normal pool conditions — it must be physically diluted or the pool drained to reduce levels.
- The recommended CYA range for residential pools is 30–50 ppm (APSP / Pool & Hot Tub Alliance). For saltwater pools, 60–80 ppm is sometimes recommended.
- CYA above 100 ppm significantly reduces chlorine effectiveness (chlorine lock), requiring much higher free chlorine levels to sanitize effectively.
- Refill water CYA is assumed to be 0 ppm unless your municipal supply contains stabilizer (rare but possible — verify with your water utility).
- The formula assumes a single drain-and-refill event with complete mixing. Real-world results may vary slightly due to incomplete mixing or residual CYA in plumbing.
- Water cost estimate uses a U.S. national average of approximately $0.004 per gallon (EPA WaterSense, 2023). Actual costs vary by municipality.
- Always retest water chemistry after refilling and allow full circulation (minimum 8–24 hours) before adding chemicals.
- Reference: Pool & Hot Tub Alliance (PHTA) Water Quality Standards; Cyanuric Acid and Chlorine Efficacy, Journal of Environmental Health, 2002.