Cyanuric acid (stabilizer): how much to add, and what to do if it's high

Doses checked 11/10/2026

Cyanuric acid, also called stabilizer or CYA, protects chlorine in outdoor pools from sunlight. Aim for 30–50 ppm, the range on the Oregon Health Authority fact sheet. The official chart from the Indiana Department of Health gives 13 oz to raise it by 10 ppm in 10,000 US gallons. It can only be lowered by draining part of the water, so add it slowly.

Checked on every build: 12 tests of the sums this calculator runs, including 1 amount printed in published charts, labels and manuals (ours must match them, or land under them where we start low on purpose) and 3 tests of its limits: caps, smaller rounds, and the cases where it gives no amount.

Read before you add anything

Never add acid and chlorine at the same time, and never mix them, even in a bucket or feeder. Mixing chlorine products with acid can create toxic gas. Add one, let the pump run, retest, then add the other.
Always add the chemical to water, never water to the chemical.
Add one chemical at a time. Never mix chemicals together, and use a separate clean scoop for each.
Add chemicals only when nobody is in the pool.
Wear the protective gear your product label asks for, such as goggles and gloves.
Handle chemicals in a well-ventilated area.
Add acid with the pump running, into the deep end, away from the skimmer and away from any floater or feeder that holds chlorine tablets.
Never add shock (cal-hypo or any other chlorine product) through the skimmer, or through any floater or feeder that holds or has held tablets, and never put different chlorine products in the same feeder.
Only pre-dissolve a chemical in a bucket if its label tells you to.
Store chemicals in a secure place away from children and pets, and never store liquid chemicals above dry chemicals.
Read the product label before each use. If the label differs from this estimate, follow the label.
These amounts are estimates. Add in stages and retest before adding more.
This tool cannot tell you the water is safe to swim in. Follow your product label, and if in doubt ask a pool professional.

Where each line comes from

CDC, Using Pool Chemicals Safely Official: “Never mix / Chlorine products with acid; this could create toxic gases” Source page (opens in a new browser tab)
12.5% liquid chlorine label, EPA-accepted Other source: “Mixing this product with chemicals (e.g. ammonia, acids, detergents, etc.) or organic matter (e.g. urine, feces, etc.)” ... “will release chlorine gas which is irritating to eyes, lungs and mucous membranes.” Source page (opens in a new browser tab)
CDC Official: “add pool chemical to water; NEVER add water to pool chemical” and “violent (potentially explosive) reaction can occur” Source page (opens in a new browser tab)
Virginia Department of Health Official: “Add chemicals to water - not water to chemicals.” Source page (opens in a new browser tab)
Indiana Department of Health Official: “Add acids to water, NEVER water to acid. Remember AAA (Always Add Acid).” Source page (opens in a new browser tab)
CDC Model Aquatic Health Code 2024, 5.9.3.4.2.3.1 Official: “Two or more chemicals shall never be mixed in the same dilution water.” Source page (opens in a new browser tab)
Indiana Official: “Never mix any chemicals together.” Source page (opens in a new browser tab)
Virginia Official: “Designate tools per chemical - Do not use the same scoop for different chemicals.” Source page (opens in a new browser tab)
MAHC 5.9.3.4.1.2 Official: “Chemicals added manually directly into the AQUATIC VENUE shall only be introduced in the absence of BATHERS.” Source page (opens in a new browser tab)
Virginia Official: “NEVER add pool chemicals when the pool is in use, and only add them poolside as directed by the product label.” Source page (opens in a new browser tab)
CDC, Using Pool Chemicals Safely Official: “Dress for safety by wearing appropriate safety equipment (for example, safety goggles, gloves, and mask)” Source page (opens in a new browser tab)
12.5% liquid chlorine label, EPA-accepted Other source: “Wear safety glasses or goggles and rubber gloves when handling this product.” Source page (opens in a new browser tab)
Alliance Trading pH Down (dry acid) label Other source: “Wear goggles or safety glasses and rubber gloves when handling this product.” Source page (opens in a new browser tab)
CDC, Using Pool Chemicals Safely Official: “Handle in a well-ventilated area” Source page (opens in a new browser tab)
Leslie's muriatic acid Other source: “With the pump running, pour the solution into the deep end of your pool, or away from the skimmer or any fixtures.” Source page (opens in a new browser tab)
Alliance Trading pH Down label Other source: “To add this product, broadcast into the deep end of the pool when not in use.” and “Do not add near metal fittings nor allow pH to drop below 7.2.” Source page (opens in a new browser tab)
CDC Official: “Never mix / Chlorine products with acid; this could create toxic gases” Source page (opens in a new browser tab)
UConn Health, Connecticut Poison Control Center, "Splish Splash Safety" Other source: “Keep acids away from other chemicals.” Source page (opens in a new browser tab)
Alliance Chemical 12.5% sodium hypochlorite safety data sheet Other source: “Never mix with acids, ammonia or other cleaning products: this releases toxic chlorine or chloramine gas.” Source page (opens in a new browser tab)
HTH Pool Care Shock, calcium hypochlorite 52% Other source: “Do not use this product in a floater or feeder.” Source page (opens in a new browser tab)
HTH 3" Chlorine Tabs Advanced Other source: “Do not use this product in floaters or feeders that have been used with other chlorinating products.” and “Do not use with any other tablets or sticks in the same skimmer, floater, or feeder.” Source page (opens in a new browser tab)
BioGuard cal-hypo label, EPA-accepted Other source: “Do not add this product to any dispensing device containing remnants of any other product.” Source page (opens in a new browser tab)
CDC Official, under “Never mix”: “Different pool chemicals (for example, different types of chlorine products) with each other or with any other substance” Source page (opens in a new browser tab)
CDC Official: “Only pre-dissolve pool chemicals when directed by product label” Source page (opens in a new browser tab)
Virginia Official: “Store chemicals in secure location away from children and pets.” Source page (opens in a new browser tab)
Virginia Official: “Never store liquid chemicals above dry chemicals.” Source page (opens in a new browser tab)
CDC Official: “Read chemical product label before each use” Source page (opens in a new browser tab)
Yakima County chart Official: “NOTE: This chart gives approximate amounts of each chemical listed. Always read the labels for exact” / “amounts needed for your chemical adjustments.” Source page (opens in a new browser tab)
Licking County Official: “Always follow instructions on the manufactures label for exact dosage amounts and handling.” Source page (opens in a new browser tab)
Multnomah County Official: “It is always better to add part of the required amount of chemical over several occasions” ... “than all at once (EXCEPTION: breakpoint chlorination).” Source page (opens in a new browser tab)
Indiana Official: “Add large amounts gradually in thirds over a 2-hour period.” Source page (opens in a new browser tab)
Our own rule for every result: we point you to your label and the official guidance instead.

What cyanuric acid does

A pool industry committee article says A certain amount of cyanuric acid (usually within the range of 30 – 50 ppm) is necessary to protect outdoor pools from degradation by sunlight. The Oregon Health Authority says The ideal range for CYA is typically between 30-50 ppm. More stabilizer means you need more free chlorine: the calculator aims for about 7.5% of your stabilizer reading (industry guidance from a pool chemical maker and a trade magazine).

How much stabilizer to add

The Indiana Department of Health chart gives Cyanuric Acid*** 13 oz 2.5 lbs 4.1 lbs for rises of 10 ppm and more in 10,000 US gallons; Yakima County (Washington) gives the same: Cyanuric Acid (Conditioner) 13 ounces. The calculator gives three quarters of the total first, or the amount for 30 ppm if that is less. Stabilizer dissolves slowly: retest only once it has fully dissolved, then work out the rest.

For example, say your pool holds 20,000 US gallons and stabilizer reads 10 ppm. To reach 30 ppm the calculator estimates 3.2 lb in all, and says to add 2.4 lb (1,085 g) now.

Stabilized chlorine adds it for you

Tablets and dichlor carry stabilizer with them. The pool industry committee article says When trichlor is used, 0.6 ppm of cyanuric acid is added to the water for each ppm of available chlorine added. Dichlor adds about 1 ppm for each ppm of chlorine, by the county charts. If you use either, test stabilizer regularly.

The chlorine you need at each stabilizer reading

Stabilizer 0 ppm2 ppm
Stabilizer 10 ppm2 ppm
Stabilizer 20 ppm2 ppm
Stabilizer 30 ppm2.5 ppm
Stabilizer 40 ppm3 ppm
Stabilizer 50 ppm4 ppm
Stabilizer 60 ppm4 ppm (capped: 7.5% would be 4.5)
Stabilizer 70 ppm4 ppm (capped: 7.5% would be 5.25)

Free chlorine the calculator aims for at each stabilizer reading: the larger of 2 ppm and about 7.5% of the stabilizer (industry guidance from a pool chemical maker and a trade magazine), rounded up to the next half ppm, and never above 4 ppm, the swimming level on most chlorine labels we checked. Where the share would be higher, the calculator says the stabilizer is too high and points you to a pool professional. Bars are drawn to scale out of 4 ppm.

If stabilizer is too high

The Oregon Health Authority says Currently, high CYA levels can only be reduced by draining a portion of the aquatic venue and refilling with fresh water. Above 50 ppm, the calculator gives no dose and suggests a partial drain; talk to a pool professional before draining, because draining can damage some pools. Above 70 ppm it sends you to a pool professional.

Official limits differ. The Licking County Health Department (Ohio) chart lists 70 ppm; CDC's model code, Oregon and Arkansas set 90 ppm; the model code says The CYA concentration at all AQUATIC VENUES shall remain at or below 90 ppm (mg/L). Other health departments give 25–40 ppm (Arkansas Department of Health) and 40–50 ppm (Maryland Department of Health) as their ranges.

Questions people ask

What is cyanuric acid?

A pool stabilizer: it protects chlorine in outdoor pools from sunlight. It is sold on its own and is also part of tablets and dichlor.

How do I raise cyanuric acid in my pool?

Add stabilizer as your label directs, in parts. By the official chart, 13 oz raises it by 10 ppm in 10,000 US gallons. Retest only once it has fully dissolved.

How much stabilizer do I add to my pool?

Enough to reach 30 ppm, or up to 50 ppm if you choose. Enter your pool size and reading in the calculator, which gives the first part to add now.

How do I lower cyanuric acid in my pool?

Only by draining part of the water and refilling. Talk to a pool professional before draining: draining can damage some pools.

How long after adding stabilizer can I swim?

We couldn't find a published figure for this. Follow your product's label, or ask a pool professional.

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The charts behind this page

Show all 14 figures and where each one comes from

Each figure this page and its calculator use. Open one for the source's own words, the other sources we checked it against, and the checks it has been through.

Ideal free chlorine range (home pool target band): 2–4 ppm Official
Licking County Health Department (Ohio): Pool and Spa Water Chemistry Adjustment Guide Official says: Free Chlorine (ppm) 1 2-4 N/A (recommended not higher than 5) Source page (opens in a new browser tab)
Also checked: Oregon Health Authority: Water Quality Standards, OAR 333-062-1000 (public pools) Official says: Free Chlorine (w/CYA) 2.0ppm 2.0-4.0ppm 10.0ppm Source page (opens in a new browser tab)
Also checked: Pentair IntelliChlor IC15/20/40/60 Installation and User's Guide, P/N 520589 Rev R Other source says: 2.0 - 4.0 ppm. Source page (opens in a new browser tab)
Also checked: HTH 3" Chlorine Tabs Advanced product page Other source says: Add one tablet per 10,000 gallons of pool water every week, or as often as needed, to maintain a free available chlorine level of 1–4 ppm. Source page (opens in a new browser tab)
Also checked: Hayward AquaRite Owner's Manual 092538 RevD Other source says: chlorine tests will show the desired 1-3ppm free chlorine reading. Source page (opens in a new browser tab)
Also checked: Arkansas Department of Health Official says: Pool* 1.0 1.0 – 3.0 5.0 Source page (opens in a new browser tab)
Also checked: Maryland Department of Health Official says: Free Chlorine 1.5 ppm 2.0 ppm – 3.0 ppm 10.0 ppm Source page (opens in a new browser tab)
Checked against the source on 11/10/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Free chlorine above which chlorine labels say do not swim (re-entry level): 4 ppm Other source
EPA-accepted label: B's Pool Supply Sodium Hypochlorite Solution 12.5% (EPA Reg. 55487-20001) Other source says: SWIMMING POOL WATER DISINFECTION – Do not reenter pool with a chlorine level above 4 ppm for risk of bodily harm. Source page (opens in a new browser tab)
Also checked: EPA-accepted label: BioGuard Master Calcium Hypochlorite 67% (Bio-Lab, EPA Reg. 5185-238) Other source says: Reentry into treated swimming pool is prohibited above levels of 4 ppm chlorine due to risk of bodily injury. Source page (opens in a new browser tab)
Also checked: EPA-accepted label: PDQ ChlorSan 8% Sodium Hypochlorite (EPA Reg. 58880-2) Other source says: Reentry into treated pools is prohibited above levels of 4.0 ppm due to risk of bodily harm. Source page (opens in a new browser tab)
Also checked: HTH Pool Care Shock product page Other source says: Do not enter the pool until free available chlorine levels return to 1–4 ppm. Source page (opens in a new browser tab)
Also checked: EPA-accepted label: Tarry trichlor 8 oz tablets/sticks (Qualco, EPA Reg. 3525-120) Other source says: Re-entry into treated swimming pools/spas is prohibited above levels of 3.0 ppm. Source page (opens in a new browser tab)
Also checked: EPA-accepted label: Tarry trichlor 8 oz tablets/sticks (Qualco, EPA Reg. 3525-120) Other source says: Do not enter pool until the chlorine residual drops to 2.0 ppm (parts per million). Source page (opens in a new browser tab)
Also checked: CDC Model Aquatic Health Code, 5th edition (2024), Code Official says: Maximum DPD-FC concentrations shall not exceed limits specified on the product label. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.
Free chlorine to keep, as a share of stabilizer (CYA): 7.5% of CYA Other source
Orenda Technologies: What is the ideal CYA level for a swimming pool? Other source says: You could go higher, but you would also need to proportionally increase your free chlorine levels ... to maintain 7.5% of your CYA level in free chlorine. Source page (opens in a new browser tab)
Also checked: AQUA Magazine Other source says: The free chlorine level should be 7.5 percent of CYA. Source page (opens in a new browser tab)
Also checked: AQUA Magazine Other source says: As an example, you add 30 ppm of CYA and you will always need about 2 ppm of free chlorine (30 ppm × .075 = 2.25 ppm). Source page (opens in a new browser tab)
Also checked: AQUA Magazine Other source says: Or if you have 50 ppm of CYA, you will need about 4 ppm of free chlorine (50 × .075 = 3.75 ppm). Source page (opens in a new browser tab)
Also checked: Trouble Free Pool forum thread 'Chlorine/CYA chart vs 7.5% of CYA' Other source says: 7.5% is essentially the FC level where chlorine kills algae faster than it can reproduce Source page (opens in a new browser tab)
Also checked: Oregon Health Authority: Fact Sheet 6, Cyanuric Acid Official says: Exceeding the CYA to free chlorine ratio of 45:1 means the chlorine is unable to kill pathogens in the water. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Ideal stabilizer (cyanuric acid, CYA): 30–50 ppm Official
Oregon Health Authority: Fact Sheet 6, Cyanuric Acid Official says: The ideal range for CYA is typically between 30-50 ppm. Source page (opens in a new browser tab)
Also checked: Licking County Health Department (Ohio): Pool and Spa Water Chemistry Adjustment Guide Official says: Cyanuric Acid (ppm) 0 30-50 70 Source page (opens in a new browser tab)
Also checked: Orenda Technologies: What is the ideal CYA level for a swimming pool? Other source says: We recommend 30-50 ppm CYA for residential pools. Source page (opens in a new browser tab)
Also checked: the PHTA pool industry committee Other source says: A certain amount of cyanuric acid (usually within the range of 30 – 50 ppm) is necessary to protect outdoor pools from degradation by sunlight. Source page (opens in a new browser tab)
Also checked: Pentair IntelliChlor IC15/20/40/60 Installation and User's Guide, P/N 520589 Rev R Other source says: 30 - 50 ppm Source page (opens in a new browser tab)
Also checked: Arkansas Department of Health Official says: Add CYA separately, only as needed, to maintain 25–40 ppm in outdoor pools. Source page (opens in a new browser tab)
Also checked: Arkansas Department of Health Official says: Anything above 50ppm CYA is considered high and can interfere with other pool chemicals' effects and equipment. Source page (opens in a new browser tab)
Also checked: Maryland Department of Health Official says: Cyanuric Acid (if used) 30 ppm 40 ppm- 50 ppm 100 ppm Source page (opens in a new browser tab)
Checked against the source on 11/10/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Stabilizer (CYA) level above which the tool says 'ask a pool professional': 70 ppm Official
Licking County Health Department (Ohio): Pool and Spa Water Chemistry Adjustment Guide Official says: Cyanuric Acid (ppm) 0 30-50 70 Source page (opens in a new browser tab)
Also checked: CDC Model Aquatic Health Code, 5th edition (2024), Code Official says: The CYA concentration at all AQUATIC VENUES shall remain at or below 90 ppm (mg/L). Source page (opens in a new browser tab)
Also checked: Oregon Health Authority: Fact Sheet 6, Cyanuric Acid Official says: The CYA level at all AQUATIC VENUES shall remain at or below 90 ppm (mg/L). Source page (opens in a new browser tab)
Also checked: the PHTA pool industry committee Other source says: If the cyanuric acid level exceeds the APSP maximum of 100 ppm, a partial drain and refi ll is recommended. Source page (opens in a new browser tab)
Also checked: Arkansas Department of Health Official says: The MAHC & ADH recommend that CYA not exceed 90 ppm for standard pools. Source page (opens in a new browser tab)
Also checked: Maryland Department of Health Official says: Cyanuric Acid (if used) 30 ppm 40 ppm- 50 ppm 100 ppm Source page (opens in a new browser tab)
Checked against the source on 11/10/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Stabilizer (CYA) added by trichlor for each 1 ppm of chlorine: 0.6 ppm CYA per ppm FC Other source
the PHTA pool industry committee Other source says: When trichlor is used, 0.6 ppm of cyanuric acid is added to the water for each ppm of available chlorine added. Source page (opens in a new browser tab)
Also checked: Trouble Free Pool forum 'Compiled info on chemicals' (first-year owner) Other source says: It will add .6 part CYA for every 1 part of chlorine it adds. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Stabilizer (CYA) added by dichlor for each 1 ppm of chlorine: 1 ppm CYA per ppm FC Official (worked out)
Worked out: Yakima: 1.6 lb = 25.6 oz raises stabilizer 10 ppm; at 2.5 oz per ppm, 25.6 oz raises chlorine 10.24 ppm; 10 ÷ 10.24 = 0.98. Salt Lake: 26 oz raises stabilizer 10 ppm; at 25 oz per 10 ppm, 26 oz raises chlorine 10.4 ppm; 10 ÷ 10.4 = 0.96. Rounded up to 1.0.
Yakima County (Washington): Chemical Dosing chart Official says: Dichlor 1.6 pounds Source page (opens in a new browser tab)
Also checked: Yakima County (Washington): Chemical Dosing chart Official says: Dichlor 2.5 ounces Source page (opens in a new browser tab)
Also checked: Salt Lake County Health Department (Utah): pool chemical dosages Official says: Dichlor 13 oz. 26 oz. Not recommended Source page (opens in a new browser tab)
Also checked: Trouble Free Pool forum 'Compiled info on chemicals' (first-year owner) Other source says: It will add .9 parts CYA for every 1 part chlorine it adds. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026.
Cyanuric acid (stabilizer, 100%): oz to raise CYA 10 ppm in 10,000 US gal: 13 oz per 10 ppm per 10,000 US gal Official
Indiana Department of Health: Adjusting Chemical Levels in a Swimming Pool / Water Chemistry Adjustment Guide Official says: Cyanuric Acid*** 13 oz 2.5 lbs 4.1 lbs Source page (opens in a new browser tab)
Also checked: Salt Lake County Health Department (Utah): pool chemical dosages Official says: Cyanuric Acid 6 ½ oz. 13 oz. 4 lb. Source page (opens in a new browser tab)
Also checked: Yakima County (Washington): Chemical Dosing chart Official says: Cyanuric Acid (Conditioner) 13 ounces Source page (opens in a new browser tab)
Also checked: Leslie's: Pool Stabilizer and Conditioner Other source says: Dosage: 2-1/2 lbs. per 10,000 gallons raises CYA level by 30 ppm Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.
Stabilizer (cyanuric acid): wait before swimming: no published figure found Not confirmed
We couldn't find a published figure for this. Follow your product's label, or ask a pool professional.
Closest we found: Virginia Department of Health says NEVER add pool chemicals when the pool is in use, and only add them poolside as directed by the product label. Source page (opens in a new browser tab)
US gallon to liters: 3.785412 L per US gal Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: gallon (U.S.) (gal) | liter (L) | 3.785 412 | E+00 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
US fluid ounce to milliliters: 29.57353 mL per US fl oz Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: ounce (U.S. fluid) (fl oz) | milliliter (mL) | 2.957 353 | E+01 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Ounce (avoirdupois) to grams: 28.34952 g per oz Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: ounce (avoirdupois) (oz) | gram (g) | 2.834 952 | E+01 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Pound to kilograms: 0.4535924 kg per lb Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: pound (avoirdupois) (lb) | kilogram (kg) | 4.535 924 | E-01 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Stabilizer can only be lowered by draining part of the water: partial drain Official
Oregon Health Authority: Fact Sheet 6, Cyanuric Acid Official says: Currently, high CYA levels can only be reduced by draining a portion of the aquatic venue and refilling with fresh water. Source page (opens in a new browser tab)
Also checked: the PHTA pool industry committee Other source says: If the cyanuric acid level exceeds the APSP maximum of 100 ppm, a partial drain and refi ll is recommended. Source page (opens in a new browser tab)
Also checked: Gohlke Pools (Denton, Texas pool builder): Should I drain my pool? Other source says: Draining a swimming pool should be a last resort. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.