Real-life case: three summers of tablets, and chlorine that no longer worked
- The situation: water turning green every late summer DESPITE perfect chlorine levels on the tests — three summers running.
- The invisible culprit: three seasons of stabilised tablets had saturated the water with stabiliser — the chlorine shown was 'locked up'.
- No product lowers the stabiliser: the only way out is partial water renewal, calculated.
- Since then: non-stabilised shocks, stabiliser curve tracked in the app — never green in September again.
It had become the curse of September. Three summers running, the same scenario: a whole season of disciplined maintenance — tablets in the skimmer, regular tests, immaculate numbers — then, in late August, the water turning green with no explanation. The tests said “chlorine: perfect”. The shocks (with stabilised chlorine, of course) pushed the green back for a week. Then a relapse. The pool technician spoke of a “tough end of season”. The forums blamed the weather. Everyone was looking at the chlorine. Nobody was looking at the number next to it.
The culprit nobody tests
The breakthrough came from the first full test in the app: every parameter, not just the usual trio. And there, a line in red alert: stabiliser (cyanuric acid): very high. Three seasons of stabilised chlorine tablets — each tablet adds a little, and it never leaves: not evaporated, not filtered, not consumed. It piles up, summer after summer.
The chemical consequence: at that level of stabiliser, the chlorine measured is massively “locked up” — present on the strip, almost inactive in the water. The pool showed 2 ppm and sanitised as if it had 0.2. The late-summer algae weren’t benefiting from a chlorine shortage: they were benefiting from chlorine in a cage. And the cruel irony: every “recovery” stabilised shock tightened the cage a little more.
The way out: fresh water, not one more product
Bad news the app owns up to: no product lowers the stabiliser. The only way out is dilution — renewing part of the water. The calculation is proportional to the gap, and the plan spread the operation out: partial drain in stages, fresh water top-ups, re-test between each. In a week of calm manoeuvres, the level was back in the healthy zone.
And the result showed immediately: at an equal displayed chlorine level, the water started to “hold” like never before — reactive sanitisation, normal consumption, the feel of lively water. The same strip figure, but unlocked.
What followed: tablets yes, blindly no
No question of giving up the tablets — too convenient. The method just gained two reflexes. Shocks with non-stabilised chlorine, systematically: it was the line item loading the boat the most. And the stabiliser curve tracked in the app, a few tests a season are enough: it rises slowly, you see it coming from far off, and a preventive off-season dilution costs three times less than a ruined summer. Two Septembers have passed since: zero curse.
What this case teaches
When water turns despite good numbers, don’t test the chlorine harder — test what you never test. The stabiliser is the pool’s most discreet saboteur: invisible, cumulative, and capable of making all the other numbers lie. One full test a month in the app, and that trap no longer springs shut: the curve warns you years before the wall, and every calculated dose takes account of YOUR stabiliser level — not a theoretical pool.
Frequently asked questions
How can chlorine be 'good on the test' yet ineffective?
The test measures the chlorine present, not its real power. With a very high stabiliser, most of that chlorine is bound and almost inactive: the figure is reassuring, the sanitisation is flat. It's the perfect trap, because everything SEEMS fine.
What proportion of water should I renew when the stabiliser is too high?
It follows the gap between your level and your target: the dilution is proportional. It's a simple calculation but one that must start from YOUR measured figure — the app does it and plans the operation.
Are chlorine tablets to be avoided?
No — they're convenient and effective, provided you KNOW they add stabiliser and you track its build-up. The golden rule: shocks with non-stabilised chlorine, and an eye on the curve a few times a season.