Cyanuric Acid Dosing Calculator
Calculate exactly how much cyanuric acid (pool stabilizer) to add to raise CYA to your target level — or how many gallons to drain if CYA is too high. Includes minimum free chlorine guidance.
Total water volume of your pool. Check your builder paperwork, or estimate: length × width × average depth × 7.48 (for a rectangular pool).
Your current cyanuric acid level from a test kit or test strips. Use 0 if you haven't added stabilizer this season.
Current level: Low (0 ppm — no stabilizer)
CYA is too low — chlorine degrades rapidly in sunlight without stabilizer.
Recommended: 30–50 ppm for standard chlorine pools. 70–80 ppm for saltwater (salt chlorine generator) pools.
Stabilizer to Add
6.67 lbs
106.7 oz · raises CYA from 0 → 40 ppm
How to add stabilizer
Pre-dissolve granular stabilizer in a bucket of warm water, then pour slowly into the pool with the pump running. Avoid adding directly to the skimmer — it can damage equipment. CYA takes 24–48 hours to fully register on test kits. Do not retest immediately.
Stabilizer dissolves slowly. Retest CYA 48 hours after adding. Once at target, keep free chlorine at or above 3 ppm.
💡About this calculator▼
Cyanuric acid (CYA) is the stabilizer that protects chlorine from being destroyed by UV sunlight. Without it, direct sunlight degrades free chlorine in as little as two hours. With too much of it, chlorine becomes significantly less effective even at normal ppm readings — a condition sometimes called chlorine lock.
This calculator tells you exactly how many pounds of stabilizer to add to raise CYA to your target level, or how many gallons to drain if your CYA is already too high. It also shows the minimum free chlorine you need to maintain at your target CYA level.
The calculator uses the standard stabilizer dosing formula: pounds to add = (target ppm − current ppm) × pool volume ÷ 120,000. This accounts for the amount of product needed to raise the entire pool volume by the desired number of parts per million. If current CYA exceeds the target, the only solution is dilution — the calculator computes the fraction of pool water to drain based on the ratio of the excess to the current level.
📐How it's calculated▼
Stabilizer to add (lbs) = (Target CYA − Current CYA) × Pool volume (gal) ÷ 120,000
Stabilizer to add (oz) = lbs × 16
Gallons to drain = (Current CYA − Target CYA) ÷ Current CYA × Pool volume
Draining removes the same fraction of CYA as water. After refilling with fresh water (0 ppm CYA), the blended CYA level drops proportionally.
Minimum free chlorine (ppm) = Target CYA × 0.075
The 7.5% rule (sometimes called the FC:CYA ratio) is the established minimum for chlorine to remain biologically effective. At 40 ppm CYA, that's 3.0 ppm free chlorine. At 80 ppm CYA, that's 6.0 ppm.
CYA status thresholds: - Below 30 ppm: Low — chlorine degrades rapidly in sunlight - 30–50 ppm: Ideal — standard chlorine pools - 51–70 ppm: Elevated — acceptable, but watch chlorine closely - 71–100 ppm: High — chlorine effectiveness is reduced; consider partial drain - Above 100 ppm: Critical — dilution required
📎Source: Pool & Hot Tub Alliance (PHTA) water chemistry standards, Taylor Technologies water testing guidelines, and Orenda Technologies CYA research
🔍Finding your inputs▼
Pool Volume: The total water volume of your pool in gallons. This is the most important input — the dose scales directly with pool volume. If you don't know your pool's volume, check your builder's paperwork or use the estimate formula: length × width × average depth × 7.48 for rectangular pools. Round or kidney pools require a different multiplier; consult your pool documentation.
Current CYA Level: Test with a CYA-specific test kit (liquid reagent type) or test strips. DPD test strips do not measure CYA — you need a dedicated stabilizer test. If you haven't added stabilizer this season and didn't over-winter with water in the pool, CYA is likely near zero.
Target CYA Level: For standard chlorine pools using liquid chlorine, cal-hypo, or dichlor, target 30–50 ppm. For saltwater pools with a salt chlorine generator (SWG), the higher chlorine demand at the cell warrants 70–80 ppm. Trichlor tablets contribute CYA over time — if you use tabs, your CYA typically drifts upward through the season and rarely needs to be supplemented.
⚠️Special situations▼
CYA does not drop after adding stabilizer — test reads the same
CYA takes 24–48 hours to fully dissolve and register on test kits, especially in cooler water. Do not add more stabilizer immediately after testing. Wait two days with the pump running, then retest. Adding a second dose too soon can overshoot significantly.
Using trichlor tablets as primary chlorine source
Each pound of trichlor adds approximately 0.6 lbs of CYA to your pool. Over a season of heavy tablet use, CYA can climb to 100+ ppm without any additional stabilizer being added. If you use a tablet feeder or floating tablet dispenser, monitor CYA monthly and expect to do a partial drain in midsummer.
Saltwater pool — SWG producing low chlorine despite normal settings
Salt chlorine generators require more free chlorine at higher CYA levels. At 80 ppm CYA, you need at least 6 ppm FC for the pool to remain properly sanitized. If your SWG is set to 60–70% but FC keeps dropping below 4 ppm with 80 ppm CYA, that is normal — increase the SWG run time or percentage before assuming the cell is failing.
CYA is above 100 ppm — pool is cloudy or chlorine demand is very high
Above 100 ppm, CYA chemically limits chlorine so severely that normal shock treatments may not work. A partial drain of 40–50% followed by a refill is the fastest recovery path. After refilling, confirm CYA is in range before resuming normal chlorination. Do not use trichlor tablets during recovery.
❓Common questions▼
What is cyanuric acid and why does my pool need it?
Cyanuric acid (CYA) is a pool stabilizer that forms a temporary bond with free chlorine, shielding it from ultraviolet light. Without stabilizer, UV from sunlight destroys 75–90% of your pool's free chlorine within two hours of exposure. With CYA at 40 ppm, the same amount of chlorine can last most of the day. Pools without stabilizer require dramatically more chlorine to stay sanitized, especially in high-sun climates.
Why does too much CYA reduce chlorine effectiveness?
The CYA-chlorine bond is reversible — chlorine molecules break away from CYA to sanitize, then rebind. But at high CYA concentrations, so much chlorine is bound at any given moment that the "free" fraction available to kill bacteria is much smaller than your test kit reads. A pool with 100 ppm CYA and 5 ppm FC has far less sanitizing power than a pool with 40 ppm CYA and 3 ppm FC. This is why the FC:CYA ratio (7.5%) matters more than the raw ppm number.
How do I lower CYA if it is too high?
The only way to lower CYA is to remove water and replace it with fresh water. There is no chemical that destroys CYA. Drain the calculated volume from the deep end of the pool (away from the main drain to avoid air lock), refill with a garden hose or water delivery service, then retest before adding anything. Cyanuric acid test kits use a turbidity method — the cloudier the mixed sample appears, the lower the CYA, which counterintuitively means the reading involves some subjectivity at low levels.
How do I test for CYA accurately?
Use a CYA-specific liquid reagent test kit (the Taylor K-2006 or similar). The test mixes a pool water sample with a melamine reagent — as you slowly add the reagent, the sample becomes milky. The reading is taken when a black dot on the test tube bottom first disappears from view. Read the tube in outdoor shade, not indoor lighting. Test strips for CYA are less reliable for precise readings; use them for trending, not for precise dosing.
Does cyanuric acid affect pH or alkalinity?
CYA is a weak acid and contributes slightly to total alkalinity readings on some test kits — the cyanurate alkalinity fraction. At 40 ppm CYA, the contribution is small (around 12–15 ppm equivalent). At high CYA levels (80+ ppm), the cyanurate contribution is large enough that some pool chemistry guides recommend subtracting it from total alkalinity when calculating carbonate alkalinity. For most practical purposes, keep CYA in the 30–80 ppm range and this effect is minor.
🔗 Related Calculators
Algaecide Dosing Calculator
Calculate exactly how much algaecide to add to your pool. Enter your pool volume and algaecide type to get the precise dose for weekly prevention, season opening, or treating an active algae outbreak.
Chlorine Dosing Calculator
Calculate exactly how much chlorine to add to your pool. Enter your pool volume, current and target free chlorine levels, and chlorine product type to get the precise dose.
Pool Shock Treatment Calculator
Calculate exactly how much pool shock or bleach you need. Supports HTH, calcium hypochlorite, and liquid chlorine for any pool size (e.g. 12,000 gallons).