CliniPool / Understand your water
Free, total, combined chlorine: finally understand your readings
- Free chlorine: the active sanitiser — IT'S the one to watch (usual pool range 1 to 3 ppm).
- Combined chlorine (chloramines): "spent" chlorine, irritating and smelly — it should stay close to zero.
- Total chlorine = free + combined. If total ≫ free, there are chloramines to destroy.
- A good chlorine reading isn't enough: pH and stabiliser decide its real effectiveness.
Three chlorine numbers on a single test — and everything clicks once you know who’s who. Free chlorine is the active sanitiser, the one that kills algae and bacteria — it’s the one to watch (usual range: 1 to 3 ppm). Combined chlorine is the chloramines: chlorine already “spent” on sweat and cosmetics, which no longer sanitises but smells strong and irritates — it should stay close to zero. Total chlorine is simply the sum of the two. The golden rule: if the total clearly exceeds the free, the gap is combined chlorine, and it needs destroying. With what, and how much? That depends on your pool — the CliniPool app does the maths.
The three numbers, in practice
Free chlorine. Your active defence. Too low, and micro-organisms multiply (green water is never far away). In summer it gets used up fast: UV, heat, swimmers.
Combined chlorine. It doesn’t appear directly on most tests: you deduce it (total − free). It’s the indicator of how “tired” the water is. Beyond a faint trace, it explains strong smells and stinging eyes — and it signals that the free chlorine is going into battle with no reinforcements.
Total chlorine. On its own, it’s misleading: a magnificent total can hide a free chlorine at zero and combined chlorine having a field day. It’s the reading as a gap that counts.
The trap: chlorine that’s present but inactive
Measuring free chlorine doesn’t guarantee it’s working. Two parameters decide its real effectiveness. The pH: too high, and most of the measured chlorine shifts into an inactive form (which the test still counts!). The stabiliser: essential against UV, but in excess it “locks up” the chlorine — the number looks good, the sanitisation is feeble. That’s the explanation behind every “my water turned even though the chlorine was perfect”. A proper diagnosis always looks at the trio chlorine + pH + stabiliser, never at chlorine alone.
Reacting to the reading
Free low, combined low: you’re simply short of sanitiser — bring the free chlorine back up, dose calculated on the volume and the gap. Free low, combined high: you need a “breakpoint” shock chlorination to burn off the chloramines — underdosed, it makes things worse; it’s THE case where precise calculation changes everything. Free high: patience and caution — let it come back down before swimming, and if you need to speed things up (an event, a planned swim), there are neutralisers to be handled by calculation, which the app manages too.
In two sentences
Watch the free, keep the combined at zero, and never trust the total alone. And remember that chlorine is never just about chlorine: pH and stabiliser decide whether it works — the app reads all three from your strip and tells you exactly what to do.
Frequently asked questions
What chlorine level should my pool have?
The usual free chlorine range for a family pool is 1 to 3 ppm (mg/L) — adjusted for stabiliser: the higher it is, the higher you need to aim to keep genuinely active chlorine. The app sets your target for YOUR pool.
My free chlorine is fine but the water is turning — why?
Two suspects: a pH that's too high and deactivates the measured chlorine, or a stabiliser that's too high and locks it up. The chlorine number alone doesn't tell you whether it's WORKING.
Why does my chlorine vanish in midsummer?
UV destroys unstabilised chlorine within hours, and heat plus bathing push up consumption. That's the stabiliser's job — at a sensible level — along with more frequent testing in summer.
Strips or drops to measure chlorine?
Both work for everyday monitoring. What matters is measuring free AND total, and reading the colours correctly — the app reads your strip from a photo to eliminate the reading error.