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Pool Stabilizer Calculator — How Much CYA to Add
Calculate how much cyanuric acid (CYA) to add when stabilizer is low, or how much water replacement is needed when CYA is above your chosen target. The calculator keeps standard outdoor-pool and salt-chlorine-generator targets separate. No sign-ups. Instant results.
💡 Quick answer — CYA dose and dilution
100% active CYA chemistry: about 13.35 oz per 10,000 gallons raises CYA by 10 ppm.
Example: a 20,000 gallon pool going from 20 to 40 ppm requires about 53.4 oz (3.34 lb) of
100% active CYA by mass balance. Packaged-product directions can round differently, so follow the label.
Common product guidance: 30–50 ppm for many outdoor chlorine pools and 60–80 ppm for many
salt chlorine generator pools.
If current CYA is above your target, the calculator estimates a partial drain/refill instead of adding more.
The added-CYA result assumes 100% active cyanuric acid. Product labels may use rounded or formulation-specific doses. Dilution results assume refill water contains 0 ppm CYA.
Example: how much stabilizer for a 20,000 gallon pool?
A 20,000 gallon pool going from 20 ppm CYA to 40 ppm needs a 20 ppm increase. Pure mass balance for 100% active cyanuric acid gives about 53.4 oz (3.34 lb).
Calculation: 20,000 gal × 3.785 L/gal × 20 mg/L ≈ 1,514 g = 53.4 oz. A packaged stabilizer may direct a different rounded dose; follow its label. For comparison, HTH's current product table uses 4 lb for a 20,000 gallon pool and a 20 ppm increase.
Stabilizer level guide
| Pool / system | Common guidance | What to do |
|---|---|---|
| Outdoor pool using stabilized chlorine | HTH: 30–50 ppm | Add only if your measured CYA is below the target used by your maintenance method. |
| Salt chlorine generator | HTH: 60–80 ppm | Use the generator manufacturer's range if it differs. |
| Above your chosen target | Do not add more CYA | Use dilution if reduction is needed. |
| Above 100 ppm | HTH warns chlorine effectiveness can be reduced | Verify the test and consider partial water replacement. |
CYA targets vary with sanitizer method and maintenance philosophy. The CYA/FC chart explains how a CYA-based chlorine operating method differs from CDC's residential minimum-chlorine guidance.
How to add cyanuric acid to your pool
Cyanuric-acid products do not all use the same application directions. Follow the label on the exact product you buy. HTH's current 100% CYA stabilizer, for example, directs addition through the skimmer with the pump running and continued circulation for 24–48 hours. Do not substitute a generic bucket or sock method when the label gives different instructions.
CYA can take time to distribute and show consistently on a test. Avoid making a second large addition before the product's stated circulation/retest interval has passed.
How chlorine type affects stabilizer levels
Liquid chlorine & cal-hypo
These are unstabilized chlorine sources and do not directly add CYA. If CYA is needed, it is added separately.
Trichlor tablets
Trichlor is stabilized chlorine, so repeated use adds CYA along with chlorine. Monitor CYA and do not keep adding separate stabilizer automatically.
Dichlor granular
Dichlor is also stabilized chlorine and adds CYA with each dose. Track CYA when it is used regularly.
Salt chlorine generators
The generator does not add CYA itself. Many salt-system programs use a higher CYA range; HTH currently lists 60–80 ppm. Follow the generator manufacturer's instructions if they differ.
If stabilized chlorine is pushing CYA above the range you want to maintain, switching to an unstabilized liquid chlorine source stops adding additional CYA.
Pool stabilizer calculator FAQs
What is the ideal stabilizer level for a pool?
There is no single CYA target for every chlorination method. HTH's current stabilizer guidance uses 30–50 ppm for outdoor pools using trichlor or dichlor and 60–80 ppm for salt chlorine generator pools. Follow your sanitizer or equipment manufacturer's range when it differs.
How much stabilizer do I add to my pool?
For 100% active cyanuric acid, pure mass balance is about 13.35 oz per 10,000 gallons for a 10 ppm increase. Packaged-product tables can round differently, so use the calculator as a chemistry estimate and follow the exact product label for dosing and application.
Can stabilizer be too high?
Yes. Higher CYA changes how much free chlorine is required by CYA-based operating methods, and HTH currently warns that levels above 100 ppm can reduce chlorine effectiveness. Verify the CYA test before making a large water replacement and use dilution when reduction is actually needed.
Do I need stabilizer in an indoor pool?
CYA's main benefit is protecting chlorine from sunlight, so that UV-protection benefit is not present in a fully indoor pool. Indoor facilities can also be subject to different local operating rules, so follow the applicable code, sanitizer instructions, and operator guidance rather than applying an outdoor CYA target automatically.
How do I lower stabilizer levels?
Water replacement is the predictable way to reduce CYA. If refill water contains essentially no CYA, the required replacement fraction is approximately (current CYA − target CYA) ÷ current CYA. The calculator performs that dilution math and links to the Pool Dilution Calculator for more detailed scenarios.
Do chlorine tablets add stabilizer?
Trichlor and dichlor are stabilized chlorine products, so they add CYA as they add chlorine. The amount added to the pool depends on product chemistry, dose, and pool volume; a statement such as “one pound adds six ounces of stabilizer to your pool” is not a meaningful pool-level dose without the pool volume. Monitor CYA when stabilized chlorine is used regularly.
How often should I test stabilizer levels?
Test CYA often enough to catch meaningful changes after water replacement, stabilizer additions, or repeated use of stabilized chlorine. Follow the instructions and retest interval for your test method; avoid assuming a fixed error such as “test strips underread by 20–30 ppm” because performance varies by product and technique.
Does stabilizer affect my chlorine dosing?
Yes. CYA protects chlorine from sunlight but also changes the FC/CYA relationship used by some residential pool-care methods. After changing CYA, use the CYA/FC Calculator to review the applicable operating target, then use the Chlorine Calculator to calculate the chemical dose needed to reach that FC level.