How do you calculate cyanuric acid adjustment?

Subtract current CYA and any planned change from the target, then add any reserve. With a 40 ppm target, 25 ppm current and no planned dose or reserve, the remaining gap is 40 - 25 = 15 ppm of stabilizer to add.

What is a good cyanuric acid level for a pool?

Outdoor chlorine pools run 30-50 ppm, saltwater pools 60-80 ppm to protect chlorine in constant sun, and indoor pools need essentially none. Most health codes cap CYA around 90-100 ppm.

How much stabilizer raises CYA by a given amount?

Roughly 13 oz of granular cyanuric acid per 10,000 gallons raises CYA about 10 ppm. Use the ppm gap here plus your volume to size the dose, and expect stabilizer to dissolve slowly over days.

How do I lower cyanuric acid?

There is no reliable chemical remover for CYA, you lower it by partial drain and refill with fresh water, or with mobile reverse-osmosis filtration. A high CYA reading means dilution, not dosing.

Why does chlorine stop working when CYA is too high?

CYA binds a share of your free chlorine into a UV-protected but slow-acting reservoir. As CYA rises you need proportionally more free chlorine to maintain the same effective sanitizing strength, roughly a 7.5% FC-to-CYA ratio.

Cyanuric acid vs free chlorine, how are they related?

CYA is the stabilizer; free chlorine is the sanitizer. They're linked by ratio, the higher your CYA, the higher the minimum free chlorine you must carry, which is why techs target CYA deliberately rather than letting it drift.

Pool, Spa & Water Treatment Chemistry calculator

Cyanuric Acid Adjustment Calculator

Cyanuric acid (CYA), or stabilizer, is the sunscreen for chlorine, it protects free chlorine from UV burn-off but also weakens chlorine's kill power as levels climb. Pool operators and route techs use this calculation to bridge a fresh CYA test and the target that matches their sanitizer type and local health code. Outdoor chlorine pools typically need 30-50 ppm; salt (SWG) pools run higher at 60-80 ppm; indoor pools and bromine systems need little or none. Get CYA too low and chlorine evaporates by midday; too high and you need painfully high chlorine to stay effective, which is why this gap matters.

What this calculator does

Calculate cyanuric acid adjustment needed from target stabilizer, current CYA, and planned treatment.
Use it before adding stabilizer, choosing sanitizer strategy, or planning dilution.
It computes the remaining cyanuric acid gap in ppm between your target and current reading after subtracting any planned stabilizer change and adding any reserve.

Formula used

Remaining CYA gap = target CYA - current CYA - planned correction + reserve

Inputs explained

Target cyanuric acid for sanitizer type: Use the target allowed for sanitizer type and local code.
Current tested cyanuric acid: Use a fresh stabilizer test.
Planned stabilizer change from dosing or dilution: Enter expected ppm from stabilizer addition or dilution.
Extra CYA reserve above minimum: Use 0 unless targeting above the minimum.

How to use the result

Use it after a fresh stabilizer test when opening a pool, switching to a salt system, or diagnosing chlorine that won't hold in sunlight.
It gives the ppm gap only, not ounces of stabilizer, and CYA can only be lowered by dilution or draining, so a negative gap can't be fixed by adding a chemical.

Current U.S. benchmarks

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Common questions

How do you calculate cyanuric acid adjustment? Subtract current CYA and any planned change from the target, then add any reserve. With a 40 ppm target, 25 ppm current and no planned dose or reserve, the remaining gap is 40 - 25 = 15 ppm of stabilizer to add.
What is a good cyanuric acid level for a pool? Outdoor chlorine pools run 30-50 ppm, saltwater pools 60-80 ppm to protect chlorine in constant sun, and indoor pools need essentially none. Most health codes cap CYA around 90-100 ppm.
How much stabilizer raises CYA by a given amount? Roughly 13 oz of granular cyanuric acid per 10,000 gallons raises CYA about 10 ppm. Use the ppm gap here plus your volume to size the dose, and expect stabilizer to dissolve slowly over days.
How do I lower cyanuric acid? There is no reliable chemical remover for CYA, you lower it by partial drain and refill with fresh water, or with mobile reverse-osmosis filtration. A high CYA reading means dilution, not dosing.
Why does chlorine stop working when CYA is too high? CYA binds a share of your free chlorine into a UV-protected but slow-acting reservoir. As CYA rises you need proportionally more free chlorine to maintain the same effective sanitizing strength, roughly a 7.5% FC-to-CYA ratio.

Last reviewed 2026-05-12.