Pool Advice & Guides › Cyanuric acid
Cyanuric acid: why there is no miracle product
When the stabiliser (CYA) saturates your water, chlorine stops working. Here, with figures, is what really works to lower it — and why renewing the water remains the safest method.
No product "destroys" cyanuric acid in a single step. The only simple and mathematically predictable method to lower it remains renewing part of the water. Solutions without draining exist (cartridges, reverse osmosis), but their result depends on the conditions of use: they are chosen case by case, not like a magic wand.
1 · The stabiliser: what is it — and why is it a problem?
Cyanuric acid (often written CYA or "stabiliser") protects chlorine from the sun's UV rays. At the right dose, it prevents chlorine from evaporating too quickly. The catch: it is not consumed and does not evaporate. It builds up with each addition of stabilised chlorine (tablets, stabilised shock chlorine).
Beyond a certain threshold (generally around 75 mg/L), the water is "saturated": the chlorine present becomes much less effective at disinfecting. This is sometimes called "chlorine lock". At this stage, adding more chlorine solves nothing — you must lower the stabiliser level itself.
2 · The three possible solutions
✔ Most reliable Water renewal You replace part of the pool water to dilute the stabiliser. Simple, immediate, result calculable in advance. ★★★★★ Predictability of the result | ◆ No draining Filter cartridges Placed in the skimmers, with progressive action according to the manufacturer. To be maintained over time; variable result. ★★★★★ Predictability of the result | ⚙ Pro solution Reverse osmosis Treatment of the pool water by a specialised installation (contractor). Keeps the water, but on quotation. ★★★★★ Predictability of the result |
The number of stars reflects the predictability of the result (the ability to say in advance how much the level will drop), not a commercial ranking.
3 · Concrete example: a 30 m³ pool
To bring the stabiliser back to the target of 75 mg/L, the volume of water to renew is calculated simply: share to renew = 1 − (target ÷ current level). The more saturated the water, the more you must renew.
| Current level | Target | Water to renew | Volume (30 m³) | Water cost* |
|---|---|---|---|---|
| 100 mg/L | 75 mg/L | 25 % | 7,5 m³ | 36,68 € |
| 150 mg/L | 75 mg/L | 50 % | 15,0 m³ | 73,35 € |
| 200 mg/L | 75 mg/L | 62,5 % | 18,75 m³ | 91,69 € |
| 250 mg/L | 75 mg/L | 70 % | 21,0 m³ | 102,69 € |
* Estimate based on a national average water + sanitation price of €4.89/m³ incl. tax (source: French Office for Biodiversity, 2025 data). The real price depends on your municipality. This does not include heating or rebalancing the new water.
4 · What about "no-draining" solutions?
Some cartridges promise to lower the stabiliser without renewing the water. It's an interesting option when draining is difficult (water restrictions, pool hard to refill), but view it clearly.
For example, the manufacturer of the Clariskim solution publishes a trial (November 2025 → January 2026) where the level drops from 141 mg/L to 78 mg/L, about a 44.7% decrease. Note: this is a result communicated by the manufacturer, to be taken as such — not an independent study. The real rate and extent depend on your pool and on following the conditions of use.
| Approach | Principle | Order of magnitude* |
|---|---|---|
| Water renewal | One-off action, immediate and calculable result | ≈ 73 € |
| Cartridges (no draining) | Consumable used over time, progressive result | ≈ 168 € / 6 |
* For a 30 m³ pool going from 150 to 75 mg/L. Renewal is a one-off, predictable expense; the cartridge is a consumable whose exact yield is not documented publicly and independently. Read as benchmarks, not a strict equivalence. Prices subject to change.
5 · Our 3 habits to avoid getting there
1 Measure the stabiliser Test the CYA a few times during the season, not just chlorine and pH. It's the one that climbs silently. | 2 Alternate your chlorines Tablets and stabilised shock chlorine add CYA. Alternating with a non-stabilised chlorine (calcium hypochlorite) slows the build-up. | 3 Renew a little, often Regularly replacing a small part of the water (backwashing, top-ups) prevents reaching saturation. |
6 · In summary
Faced with a saturated stabiliser: economical and immediate solution — renew part of the water when possible; no-draining solution — cartridges, following the manufacturer's instructions, if draining isn't possible; professional solution to keep the water — reverse osmosis, on quotation.
The common thread: don't count on a "miracle product". The right reflex is to monitor the level and act before saturation.
French Office for Biodiversity — Observatory of public water and sanitation services (water prices).
Clariskim — product information, usage tips and manufacturer trial (result communicated by the manufacturer).
Prices and availability for information only, subject to change. Informational page, not a guarantee of results.