01
The purpose
What does this calculator estimate?
How much stabilizer to add — or how much to drain to lower CYA — plus the minimum chlorine your CYA level needs.
Water Chemistry · B6
Cyanuric Acid (CYA / Stabilizer) Calculator
How much stabilizer to add — or how much to drain to lower CYA — plus the minimum chlorine your CYA level needs.
Measure the inputsCYA dissolves very slowly — use a skimmer sock and squeeze it, don't dump granules on the floor.
Read the full resultHigher CYA protects chlorine from sunlight but raises the minimum FC you must maintain.
Check the boundaryTrichlor and dichlor add CYA every time you use them — test CYA monthly if you rely on tablets.
Useful forWater ChemistryPlanningComparisonVerification
Live calculation
Cyanuric acid adjustment
✓ Checked May 2026
Enter current and target CYA.
Recommended dose
—
Enter the required values to calculate.
Enter the known values. Let the engine handle the calculation.
✓ Formula checked↻ Live result○ No account needed
Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.
The result, explained
Use the Cyanuric Acid (CYA / Stabilizer) Calculator result with context.
How much stabilizer to add — or how much to drain to lower CYA — plus the minimum chlorine your CYA level needs.
02
The tool
What information does it use?
- Pool volume: enter a measured or verified value
- Current cyanuric acid: From your test kit, in ppm.
- Target cyanuric acid: Chlorine pools 30–50 ppm; salt pools 60–80 ppm.
- Addition method: Skimmer sock or pre-dissolve — CYA is slow to dissolve.
03
The method
How to use this calculator
- Pool volumeEnter the value you can verify.
- Current cyanuric acidFrom your test kit, in ppm.
- Target cyanuric acidChlorine pools 30–50 ppm; salt pools 60–80 ppm.
- Addition methodSkimmer sock or pre-dissolve — CYA is slow to dissolve.
04
The relationship
The formula in plain English
Raise: Dose = (CYA change ÷ 10) × (Volume ÷ 10,000) × 13 oz stabilizer
Min FC = CYA × 0.075 · SLAM FC = CYA × 0.4. Lowering CYA requires partial draining.05
Worked through
A worked example: 15,000 gal pool, raise CYA 20 → 50 ppm
- CYA increase = 50 − 20 = 30 ppm
- Dose = (30 ÷ 10) × (15,000 ÷ 10,000) × 13 oz = 58.5 oz
- 58.5 oz ÷ 16 = ~3.7 lb stabilizer in a skimmer sock
| Pool volume | Stabilizer (+10 ppm CYA) | CYA level | Min FC needed | SLAM FC |
|---|---|---|---|---|
| 10,000 gal | 1.3 lb | 30 ppm | 2.3 ppm | 12 ppm |
| 15,000 gal | 1.9 lb | 40 ppm | 3.0 ppm | 16 ppm |
| 20,000 gal | 2.6 lb | 50 ppm | 3.8 ppm | 20 ppm |
| 25,000 gal | 3.3 lb | 60 ppm | 4.5 ppm | 24 ppm |
| 30,000 gal | 3.9 lb | 70 ppm | 5.3 ppm | 28 ppm |
| 40,000 gal | 5.2 lb | 80 ppm | 6.0 ppm | 32 ppm |
06
Why it matters
How the result supports the next decision
CYA dissolves very slowly — use a skimmer sock and squeeze it, don't dump granules on the floor.
Higher CYA protects chlorine from sunlight but raises the minimum FC you must maintain.
07
Good inputs
Improve the estimate before relying on it
- CYA dissolves very slowly — use a skimmer sock and squeeze it, don't dump granules on the floor.
- Higher CYA protects chlorine from sunlight but raises the minimum FC you must maintain.
- Trichlor and dichlor add CYA every time you use them — test CYA monthly if you rely on tablets.
- The only way to lower CYA is to drain and refill; no chemical removes it.
- Match your minimum daily FC to your CYA: about 7.5% of CYA is the sanitization floor.
08
The boundary
How to interpret the result
Follow the product label, add chemicals separately and retest before another dose.
The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.
09
Before acting
What should override this estimate?
- Measured site conditions and current test results
- Product labels and manufacturer specifications
- Qualified-professional advice and applicable local codes
10
Common questions
Frequently asked questions
What does cyanuric acid do in a pool?
Cyanuric acid (CYA), also called stabilizer or conditioner, shields free chlorine from being destroyed by the sun's UV rays. Without it, an outdoor pool can lose most of its chlorine within hours. The trade-off is that higher CYA requires you to hold a higher minimum free chlorine.
What CYA level should my pool have?
Traditional chlorine pools run 30–50 ppm. Saltwater pools usually want 60–80 ppm because the generator drips chlorine slowly all day and benefits from extra UV protection. Indoor pools need little or no CYA since there's no sunlight.
How do I lower cyanuric acid?
There's no chemical that removes CYA — you lower it by draining part of the pool and refilling with fresh water. The calculator shows what percentage to replace. CYA-reducing media products exist but are slow and costly compared to dilution.
Why does my CYA keep rising?
If you use trichlor tablets or dichlor granules, every dose adds cyanuric acid. Over a season this can push CYA well above 80 ppm, at which point chlorine becomes sluggish. Switching to liquid chlorine or cal-hypo stops the climb.
What is the FC to CYA ratio?
Free chlorine must scale with CYA to stay effective. The minimum FC is roughly 7.5% of your CYA — so a 40 ppm CYA pool needs at least 3 ppm FC. For shocking algae, the SLAM target is 40% of CYA.
How much stabilizer to raise CYA 30 ppm?
About 3.9 lbs per 10,000 gallons. For a 15,000-gallon pool, that's roughly 5.9 lbs of cyanuric acid to raise CYA by 30 ppm.
Can CYA be too high?
Yes. Above about 80–100 ppm, chlorine becomes increasingly locked up and slow to sanitize, and you'd need impractically high FC. The fix is dilution by partial draining.
Does liquid chlorine add CYA?
No. Liquid chlorine (sodium hypochlorite) and cal-hypo add no stabilizer. Only trichlor and dichlor raise CYA.
Primary sources
Use the result with current guidance.
These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.