Pool CYA Stabilizer Calculator
Pool stabilizer dose from volume and CYA gap, with 30 to 50 ppm guidance.
What it does
Cyanuric acid shields outdoor chlorine from sunlight: without it most free chlorine breaks down within an hour, while 30 to 50 ppm stretches sanitizer life 3 to 4 times. Too much reverses the deal and locks chlorine into weak kill times.
The tool above takes pool volume with current and target CYA. It returns the dry stabilizer dose in two units with step dosing or drain guidance.
The default 20,000 gallons rising 10 to 40 ppm needs 78 oz (4.9 lb), half now and half after retest. The metric mirror of 75.71 cubic meters reads 2,211 g.
Dosing follows CDC pool guidance with Pool and Hot Tub Alliance fact sheets behind it. Both pin the 30 to 50 ideal band and the 100 ppm ceiling used here.
How to use
- Pick gallons or cubic meters.
- Enter the pool volume.
- Enter current CYA from a test.
- Enter target CYA, 40 is typical.
- Read the dose first, then the alt unit.
- Add half, retest in 5 to 7 days.
Formula
- gallons
- Pool volume in gallons.
- current
- CYA now, ppm.
- target
- CYA goal, 30 to 50 outdoors.
- 13 oz
- Label rate per 10 ppm per 10,000 gallons.
The 13 oz label rate matches ppm math (10 mg/L over 10,000 gallons is 378.5 g, about 13.35 oz). Metric converts cubic meters to gallons first (x 264.172), then runs the same math. Add half first and retest; never round up past target.
Worked example
Example: raise 10 to 40 ppm
Imperial defaults: 20,000 gallons, current 10 ppm, target 40 ppm.
- Rise needed: 40 - 10 = 30 ppm.
- Units of 10 ppm: 30 / 10 = 3.
- Base: 3 x 13 oz = 39 oz per 10,000 gallons.
- Volume factor: 20,000 / 10,000 = 2.
- Total: 39 x 2 = 78 oz.
- Pounds: 78 / 16 = 4.9 lb.
- Tool shows 78 oz dry stabilizer, 4.9 lb, add half now (39 oz).
Reference table
| Level | Band | Action |
|---|---|---|
| 0 to 10 ppm | Unprotected | Raise toward 30 in steps |
| 30 to 50 ppm | Ideal | Hold with monthly tests |
| 100 ppm | Ceiling | Stop adding, plan drain |
| 300 ppm | MAHC action | Immediate remediation |
Limits
- Outdoor pools only; never spas or indoor pools.
- Granular 100% CYA math; liquids differ.
- Kill times lengthen as CYA rises.
- pH and free chlorine need their own tests.
Common mistakes
- Adding through a stopped skimmer.
- Retesting before full dissolve.
- Rounding up past target.
- Chasing CYA with stabilized chlorine.
- Ignoring tablet-driven CYA creep.
Try it yourself
Quick checks. Answers sit tucked under each question.
Current 40, target 40?
Already at target: 0 oz, add none, retest monthly.
Current 120, target 40?
(120 - 40) / 120 = 67%: drain about 67% and refill, then retest.
10,000 gallons, 10 to 30 ppm?
Rise 20: 2 x 13 x 1 = 26 oz (1.6 lb).
Questions
What CYA level should a pool hold?
30 to 50 ppm outdoors. Under 30 burns chlorine fast; past 100 locks it; 300 needs immediate action.
How much stabilizer per 10 ppm?
13 oz of dry stabilizer per 10,000 gallons per 10 ppm rise. Scale linearly with volume.
How do I lower high CYA?
None. No chemical lowers CYA: drain (current - target) / current of the water and refill.
Do chlorine tablets raise CYA?
Yes. Trichlor and dichlor add CYA with every dose, so retest monthly even without adding stabilizer.
Does a hot tub need stabilizer?
No. CDC advises against CYA in hot tubs and indoor pools, where sunlight never threatens chlorine.
How long does stabilizer take to show?
Five to 7 days with the pump running. Retest only after full dissolve, then add the balance.