Cyanuric Acid Calculator
Exact ounces of stabilizer to raise CYA — or exact gallons to drain when you're over. Plus the math on what every chemical decision costs you in chlorine, and the season-long staircase trichlor builds without telling you.
Why CYA is the one-way valve of pool chemistry
Cyanuric acid is the only pool chemical with a one-way valve. Chlorine gets used up. pH drifts back. But stabilizer just sits there.
Every scoop you add, and every trichlor tab you've ever floated, stays in the water until you physically remove the water. That's why "my chlorine stopped working" and "my CYA is 120" are usually the same sentence.
Here's the deal: this calculator handles both directions. Raising? You'll get the exact ounces of stabilizer and the sock trick that keeps it out of your filter. Too high? You'll get the only honest answer — exactly how many gallons to swap — plus the math on what those trichlor tabs have been quietly depositing all season.
What you'll give us
Three numbers: pool volume, current CYA, target. The diagram below shows the raise path on the left (sock-and-return-jet) and the lower path on the right (partial drain), plus the five brand-preset chips with their honesty labels visible.
The calculator
Pick a target chip or type one in, fill the rest, hit calculate. Setting a target below your current reading auto-switches to the LOWER (dilution) plan — no separate mode toggle needed.
Raise or lower your CYA
Picking a target below your current reading auto-switches to the LOWER (dilution) plan.
Don't know your gallons? Pool volume calculator — two minutes, any shape, deep-links straight back here.
Why CYA only goes up
Three ways in, one way out. Granular stabilizer goes in by the scoop. Trichlor tabs go in by the puck. Dichlor granules go in by the handful. All three add cyanuric acid.
The only way out is water leaving the pool — drained, backwashed, splashed, or leaked. Evaporation removes water but leaves the cyanuric acid behind, the same physical-chemistry reason salt concentrates in a hot August. There is no scoop for the other direction.
Practical consequence:CYA is the one-way valve of pool chemistry. Track every input. Meter your trichlor. Test before you dose. Because once you're at 120 ppm, the only honest answer is a partial drain — and that costs real money and time.
The 8× spread nobody talks about
Three big SWG manufacturers, three different ideal CYA targets, in three different installation manuals on file. The disagreement is the story — and any calculator that quotes a single "ideal" number is hiding it.
Intex
Krystal Clear CS2110
10–30 ppm
manufacturer manual
CS2110 manual p.14 + p.8
F6
Pentair
IntelliChlor IC15/20/40/60
30–50 ppm · target 40
manufacturer manual
IntelliChlor manual p.10 + p.13–14
F15
Hayward
AquaRite
80 ppm · no range
manufacturer manual
AquaRite manual p.5–6 + dosing chart
F14
The headline
8× spread from 10 → 80 ppm
Across three manufacturer manuals on file, within a single equipment category (salt chlorine generators). There is no universal number. Follow YOUR system's manual — that's the rule that survives all three.
Broader industry context
Layer on the conventions and you'll see the manufacturer-manual spread doesn't collapse — it widens.
| System | Range | Honesty label | Source |
|---|---|---|---|
| Outdoor manual chlorination | 30–50 ppm | convention | PHTA-aligned product labels (F4) |
| SWG in-ground community practice | 60–80 ppm | derived practice | popularised by Trouble Free Pool (F5) |
| Indoor | 0–20 ppm | operator practice | no UV exposure |
| Public pools | pending | MAHC | F7 — omitted until the CDC MAHC PDF is verified |
The candor is the differentiator. None of these numbers are wrong — they describe different systems. A big in-ground SWG cell makes chlorine fast and benefits from a heavy CYA blanket; manual chlorination lives comfortably at 30–50; Intex's little 2 g/h cell can't outrun a thick blanket, so Intex caps it at 30 and accepts more UV loss.
The rule that survives every row: follow YOUR system's manual, and remember every point of CYA raises the chlorine you must carry — see the chlorine calculator for the math on the FC implications.
What stabilizer costs you in chlorine
Every point of CYA you add raises the chlorine you have to carry. That's not opinion — it's the cyanurate equilibria from the published literature. The practical rule from those equilibria: keep free chlorine at about 11.5% of your CYA, with a minimum of 7.5%.
At CYA 30 the target is about 3.5 ppm FC; at CYA 50 it's about 6 ppm; at CYA 80 it climbs to 9 ppm. Stabilization protects your chlorine from UV — and demands more chlorine to do the same sanitation. The trade-off doesn't go away by ignoring it.
One number to remember: +10 ppm CYA ⇒ ≈ +1.15 ppm FC required, every day, for the rest of the season. The chlorine calculator plots this from the same function the chart below uses — both pages can't disagree because they share lib/dosing/cya.ts.
lib/dosing/cya.ts— the same function the chlorine calculator uses. Add 10 ppm to your CYA and the target FC line jumps about 1.15 ppm; that's the price tag on stabilization, paid in chlorine for every day the rest of the season.Worked examples — eight scenarios
Eight scenarios that cover the page's search intent: spring startups, top-ups, salt-pool blankets, the high-CYA fix, the season staircase, metric, the Intex trust-anchor, and indoor pools.
Example 1
How much stabilizer to add to a pool: 15,000 gallons, 0 → 40 ppm
15,000 gal, current 0 ppm, target 40 ppm. Δ40.
5.0 lb (80 oz / 2.27 kg)
40 × 15,000 × 8.345×10⁻⁶ = 5.0 lb pure CYA — granular stabilizer is ≈100% CYA so no purity divisor.
Spring startup on a fresh fill. Sock it in front of a return jet, squeeze it occasionally for a day, then wait the week before retesting. Impatient retesting is the path to CYA 100.
Example 2
Cyanuric acid calculator: topping up from 30 to 50 ppm (10,000 gal)
10,000 gal, current 30, target 50. Δ20.
1.67 lb = 26.7 oz
20 × 10,000 × 8.345×10⁻⁶ = 1.67 lb. The interesting line is what this does to your chlorine target: at CYA 50, target FC is 6 ppm (11.5% rule — same number the chlorine calculator computes, by construction).
The dose is small; the chlorine consequence is the real line item. CYA 30 → 50 means roughly 1–2 ppm more FC required every day, forever.
Example 3
Stabilizer for a salt water pool: 25,000 gallons, 40 → 70 ppm
25,000 gal, current 40, target 70. Δ30.
6.26 lb (2.84 kg)
30 × 25,000 × 8.345×10⁻⁶ = 6.26 lb. Required FC target moves from 4.5 ppm (at CYA 40) up to 8 ppm (at CYA 70).
The SWG "blanket" strategy with its price tag printed. Big cells can carry the extra FC; small Intex-class cells cannot — which is why Intex caps the range at 30.
Example 4
Cyanuric acid too high: lowering 120 → 50 ppm (18,000 gal)
18,000 gal, current 120, target 50.
58.3% swap = 10,500 gallons
Replace fraction = 1 − (50 ÷ 120) = 58.3%; 58.3% × 18,000 = 10,500 gal of drain-and-refill.
Yes, that's most of the pool — do it in two or three rounds with retests between (see the dilution rounds diagram below). This is why we meter trichlor instead of discovering it in August.
Example 5
How fast do trichlor tabs raise CYA? (the season staircase)
12,000 gal pool, tabs covering a measured 2 ppm FC/day for 120 days.
+146 ppm CYA
240 ppm of FC delivered × 0.61 CYA-per-FC = +146 ppm CYA as an upper bound (ignores splash-out and backwash). The 0.61 constant lives once in lib/dosing/chemicals.ts — same source the chlorine page uses for its side-effect ledger.
A pool that started at CYA 30 finishes the season near 176 — the one-way valve, illustrated. Tab-strategy math lives on the chlorine tablets page (shipping in a later phase).
Example 6
Pool stabilizer calculator in kg: 45 m³ metric example
45 m³ (45,000 L), current 0, target 40 ppm.
1.8 kg
SI keeps it embarrassingly clean: kg = Δppm × m³ ÷ 1,000 = 40 × 45 ÷ 1,000 = 1.8 kg. No 8.345 to remember.
For EU/AU readers running 45,000 L pools, one 1.8 kg sock and the standard wait gets you to your starting CYA.
Example 7
Intex pool cyanuric acid: matching the manual (12'×30" example)
12'×30" Metal Frame / Prism Frame at 1,718 gal (Intex CS2110 manual p.7, 90% fill convention), target startup 10 ppm CYA per the same manual p.8 cyanuric acid table.
2.29 oz (65 g)
Our engine: 10 × 1,718 × 8.345×10⁻⁶ = 0.143 lb = 2.29 oz (65 g). Intex's own table: 2.3 oz (65 g). Agreement to the gram.
When our formula reproduces the manufacturer's table to the gram, you can trust both. The engine output above is computed live by the same function the calculator uses — drift would show up here first.
Example 8
Do indoor pools need cyanuric acid?
Indoor pool, no direct sun, no UV photolysis of chlorine.
Target 0 ppm
Some operators run up to 20 ppm for chlorine-smell management; public-pool rules may differ (CDC MAHC; specific number pending PDF verification).
CYA is sunscreen. Indoors there's no sun. Without CYA, the unstabilized FC targets apply (1–4 ppm label convention) — that's the CYA-0 row on the chlorine page's FC/CYA grid.
The trichlor staircase
Tabs are "set and forget" — except the CYA never forgets. Every 10 ppm of chlorine your tabs deliver also deposits about 6.1 ppm of permanent stabilizer.
Run the season math at 2 ppm FC/day for 120 days and a 12,000 gal pool delivers 240 ppm of free chlorine total — depositing +146 ppm of CYA. A pool that started spring at CYA 30 finishes near 176.
Upper bound, honestly:real pools knock some of that CYA off through splash-out and backwash, so the curve below is the worst case. But a tab-fed pool that doesn't get dilution somewhere along the way ends the season in the high-CYA trap — the price tag on every chemical decision for the next six months.
Lowering CYA — two rounds, retest between
Take worked example 4: an 18,000 gal pool at CYA 120, targeting 50. Single-shot math says drain 58.3% — 10,500 gallons — and refill. That works on paper.
Two partial drains is safer. Round one knocks 120 down to ~78 (drain 6,300 gal ≈ 35%). Round two takes 78 → 50 (drain 6,462 gal ≈ 36% of the now-refilled water). About 12,800 gal total — a couple thousand more than the one-shot, paying for the safety margin against overshoot.
Why two rounds:the first retest gives you a checkpoint. If round one's test comes back at 78 you continue; if it comes back at 90 (because the pool wasn't fully mixed or your test had drift) you stop and re-evaluate. With one giant drain there's no checkpoint — you find out next week.
A note on CYA reducer products
CYA reducer products (mostly enzyme/melamine-based) show inconsistent results in independent testing, so we don't put a dose behind them — a partial drain is the method with predictable math. If you've had a reducer work, great; we won't calculate one because the evidence isn't there to give you a number we trust.
Reference tables
Two tables you can cite directly. Both released under CC BY 4.0 — reuse them with a link back.
T1 · Stabilizer doses by pool volume and Δppm
All values derived from the master formula: lb = Δppm × gallons × 8.345×10⁻⁶ (CRC water density 8.345 lb/gal at 60 °F; granular CYA ≈100% so no purity divisor).
| Pool volume | Δ10 ppm | Δ20 ppm | Δ30 ppm | Δ40 ppm |
|---|---|---|---|---|
| 5,000 gal | 0.42 lb6.7 oz · 0.19 kg | 0.83 lb13.4 oz · 0.38 kg | 1.25 lb20.0 oz · 0.57 kg | 1.67 lb26.7 oz · 0.76 kg |
| 10,000 gal | 0.83 lb13.4 oz · 0.38 kg | 1.67 lb26.7 oz · 0.76 kg | 2.50 lb40.1 oz · 1.14 kg | 3.34 lb53.4 oz · 1.51 kg |
| 15,000 gal | 1.25 lb20.0 oz · 0.57 kg | 2.50 lb40.1 oz · 1.14 kg | 3.76 lb60.1 oz · 1.70 kg | 5.01 lb80.1 oz · 2.27 kg |
| 20,000 gal | 1.67 lb26.7 oz · 0.76 kg | 3.34 lb53.4 oz · 1.51 kg | 5.01 lb80.1 oz · 2.27 kg | 6.68 lb106.8 oz · 3.03 kg |
| 25,000 gal | 2.09 lb33.4 oz · 0.95 kg | 4.17 lb66.8 oz · 1.89 kg | 6.26 lb100.1 oz · 2.84 kg | 8.35 lb133.5 oz · 3.79 kg |
| 30,000 gal | 2.50 lb40.1 oz · 1.14 kg | 5.01 lb80.1 oz · 2.27 kg | 7.51 lb120.2 oz · 3.41 kg | 10.01 lb160.2 oz · 4.54 kg |
A 10,000 gal pool needs 0.83 lb / 13.4 oz / 0.38 kg per 10 ppm bump — the citable anchor. Scale linearly with both volume and Δppm; no exceptions.
T2 · CYA target ranges by system
Each row carries its honesty label. Manufacturer manual binds you for that brand; convention reflects label tradition; derived practice reflects community consensus.
| System | Range / target | Honesty label | Source | Fact |
|---|---|---|---|---|
| Intex Krystal Clear SWG | 10–30 ppm · startup 10 | manufacturer manual | CS2110 p.14 + p.8 | F6 |
| Pentair IntelliChlor SWG | 30–50 ppm · target 40 | manufacturer manual | IntelliChlor manual p.10 + p.13–14 | F15 |
| Hayward AquaRite SWG | 80 ppm · no range | manufacturer manual | AquaRite manual p.5–6 + dosing chart | F14 |
| Outdoor manual chlorination | 30–50 ppm | convention | PHTA-aligned product labels | F4 |
| SWG in-ground community practice | 60–80 ppm | derived practice | popularised by Trouble Free Pool | F5 |
| Indoor | 0–20 ppm | operator practice | no UV exposure | — |
| Public pools | pending | MAHC | CDC MAHC PDF pending verification | F7 |
The 8× spread (Intex 10 → Hayward 80) is the headline; the public-pool row is intentionally visible as "pending" because the gap belongs in the open, not buried.
Methodology & sources
Dosing on this page is the same mass-balance arithmetic as every chemical on PoolSolver: lb solute = Δppm × gallons × 8.345×10⁻⁶, anchored to the CRC Handbook's water density at 60 °F. Cyanuric acid's molecular identity (C₃H₃N₃O₃, MW 129.07) comes from PubChem; granular stabilizer is ≈100% CYA so there's no purity divisor in the formula.
Target ranges are quoted with their pedigree attached. 30–50 ppm is the outdoor-manual-chlorination convention from PHTA-aligned product labels. 60–80 ppm is salt-pool derived practice from Trouble Free Pool. 10 / 40 / 80 ppm come from the Intex, Pentair, and Hayward installation manuals sitting in our source files. We show you which kind of authority each number carries rather than averaging them into mush.
The chlorine-demand consequence of stabilizer uses the published cyanurate–chlorine equilibria (O'Brien, Morris and Butler, 1974; analysed in Wojtowicz's papers). The practical 11.5%/7.5% form lives in lib/dosing/cya.ts— the same function the chlorine calculator uses — so the two pages can't disagree by construction.
The trichlor staircase math derives from the molecular-weight ratio for trichlor → CYA: 0.61 ppm CYA per ppm FC delivered. That constant lives once, in lib/dosing/chemicals.ts, and is imported by every page that cites it. Public-pool CYA maximums come from the CDC Model Aquatic Health Code; we omit the specific number until the current MAHC PDF is verified.
Where a product category lacks verifiable efficacy data — CYA reducer products — we say so and decline to put a dose behind it. Verified or omitted, applied to a product category instead of a single number.
Sources used on this page
- CRC Handbook of Chemistry and Physics— water density 8.345 lb/gal at 60 °F (the conversion at the heart of the mass-balance formula).
- PubChem— cyanuric acid (C₃H₃N₃O₃, MW 129.07) molecular identity and physical properties; trichlor and dichlor molecular weights for the staircase derivation.
- O'Brien, Morris & Butler (1974), cyanurate–chlorine equilibria — primary literature behind the FC/CYA targeting rule; Wojtowicz's analyses derive the practical 7.5%/11.5% percentages.
- Intex CS2110 Krystal Clear Saltwater System manual— CYA recommended range (10–30 ppm) at p. 14 and per-pool startup-dose table + the 0.35%-of-salt rule at p. 8. The CYA table at p. 8 is also the source for E7's 2.3 oz / 65 g trust anchor.
- Pentair IntelliChlor IC15/IC20/IC40/IC60 manual (P/N 520589 Rev. R)— CYA recommended range 30–50 ppm (p. 10 Optimum Conditions table) and target 40 ppm (p. 13–14 Table 1 + caption).
- Hayward AquaRite manual— CYA target 80 ppm with no range stated (p. 5–6 water-chemistry section + the dosing chart headed "POUNDS and (Kg) OF STABILIZER (CYANURIC ACID) NEEDED FOR 80 PPM").
- PHTA-aligned product labels— the 30–50 ppm outdoor-manual-chlorination convention (F4).
- Trouble Free Pool community practice— the 60–80 ppm derived-practice range for in-ground SWG pools (F5); also the popularised form of the 11.5%/7.5% FC/CYA rule.
- CDC Model Aquatic Health Code— public-pool maximum CYA. The calculator does not display an MAHC number until the current PDF is verified against our facts table (F7).
Reference tables T1 and T2 above are released under CC BY 4.0. Reuse them anywhere — just attribute PoolSolver and link back.
Frequently asked questions
How much cyanuric acid to add per 10,000 gallons?
About 0.83 lb (13.4 oz / 0.38 kg) raises 10,000 gallons by 10 ppm. The math: 10 × 10,000 × 8.345×10⁻⁶ = 0.83 lb. Use the sock method and wait a week before retesting — granular CYA dissolves slowly, and impatient retesting is the path to CYA 100.
What should my CYA level be?
It depends on your system. Three of the biggest SWG brands disagree by 8×: Intex 10–30 ppm, Pentair 30–50 (target 40), Hayward 80 ppm— each from that manufacturer's own manual. The outdoor-manual-chlorination convention is 30–50; the salt-pool community practice is 60–80. Follow YOUR equipment's manual.
How do I lower cyanuric acid?
Dilution only. Replace fraction = 1 − (target ÷ current). For 120 → 50 in 18,000 gal, that's 58.3% = 10,500 gallons of drain-and-refill — done in two rounds with retest between (see the dilution rounds diagram above). CYA reducer products show inconsistent results in independent testing; a partial drain is the method with predictable math.
Does cyanuric acid evaporate or go away on its own?
No. Cyanuric acid is non-volatile and stable on homeowner timescales — it leaves only with water that leaves the pool (drain, backwash, leak, big rain with overflow). Evaporation removes water but leaves the CYA behind, which is why the one-way-valve framing fits.
Why won't my chlorine work at high CYA?
Cyanuric acid binds most of your chlorine and holds it in reserve, shielded from UV. But held-in-reserve chlorine isn't killing anything. Practical rule: keep FC at about 11.5% of CYA, minimum 7.5%. Every +10 ppm CYA requires about +1.15 ppm FC, for the rest of the season. The chlorine calculator plots this from the same function this page uses.
How long after adding stabilizer can I test?
Up to a week. Granular CYA dissolves slowly — undissolved granules don't show on the test, so impatient retesting reads low and tempts you to double-dose. Sock the dose in front of a return jet, squeeze it occasionally for a day, then wait the week before testing.
Do salt water pools need more stabilizer?
Often yes for big in-ground cells — 60–80 ppm is the community-derived practice. But notfor Intex-class systems: Intex's CS2110 manual caps CYA at 10–30 ppm because the small cell can't keep up with a thick stabilizer blanket. Follow your equipment manual; there is no universal salt-pool CYA number.
Do indoor pools need stabilizer?
No — there's no UV indoors, so there's nothing for CYA to shield against. Some operators run up to 20 ppm for chlorine-smell management; public-pool rules may differ (CDC MAHC; specific number pending PDF verification). Without CYA, the unstabilized 1–4 ppm FC label convention applies.
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