Total Chlorine
Every bit of chlorine in the water, working or spent. On its own it is not a verdict — its job is to reveal the part that is spent.
- Measured in
- mg/L
No band, deliberately. No published standard limits total chlorine; what is limited is the difference between this and free chlorine, which is judged on the Combined Chlorine guide.
What it is
Total chlorine is everything a chlorine test can see: the free chlorine still available to sanitise, plus the combined chlorine that has already reacted with sweat, sunscreen and organic debris and can no longer do much. Because it adds those two together, a healthy pool and a badly used-up one can report the same total. The number becomes useful the moment you have free chlorine beside it, because the gap between them is the part that has been spent.
Why it matters
Nothing published sets a limit on total chlorine, and that is not an oversight — the limit is on the difference between this reading and free chlorine, which is combined chlorine. Recording total is how that difference can be worked out at all. It is the one parameter here whose whole value is arithmetic on another one.
How to measure it
Any kit that reads free chlorine will read total chlorine too, usually with a second reagent or a second pad. Take both on the same sample, at the same moment — that is the whole point of the reading.
Liquid reagent kit, colour match
- How trustworthy
- Dependable
- Cost
- Low cost
- Effort
- A couple of minutes, at a sink or poolside
A measured sample in a plastic comparator block, a few drops of reagent, and a colour you match against printed standards beside the tube. The two-tube kit sold everywhere for pools is this.
The DPD test run a second time: the same pink chemistry, with a second tablet or powder that also develops the combined chlorine. Most two-tube pool shop kits can do it, though the instructions often bury it.
Watch out: Read the free chlorine first and do not let the sample stand. Combined chlorine keeps developing colour for a minute or two, so a free chlorine reading taken late drifts upward and shrinks the gap you are testing for.
Where to find it: Pool shops and online. Reagents expire, so buy replacement bottles rather than a whole new kit each season.
Drop-count titration kit
- How trustworthy
- Dependable
- Cost
- Low cost
- Effort
- A few minutes, and it rewards being unhurried
Add reagent one drop at a time until the sample changes colour, and count the drops. The count is the answer, so there is no colour to judge by eye and no lighting to get wrong.
FAS-DPD is the kit that makes this parameter easy: it counts drops for free chlorine, then you add a third reagent and keep counting for total. The two numbers come off one sample with no colour matching, which is exactly what this comparison needs.
Where to find it: Pool shops and online, usually as part of a multi-test kit. Aquarium shops sell the same chemistry in smaller bottles.
Test strips
- How trustworthy
- Ballpark
- Cost
- Low cost
- Effort
- Under a minute, wherever you drew the sample
A plastic strip with reagent pads on it. Dip it, hold it level, and match each pad against the chart on the bottle at the time the label tells you to. Most strips read several parameters at once.
Many strips print a total chlorine pad beside the free chlorine one. Good enough to notice a wide gap; not good enough to measure a narrow one.
Watch out: Both pads are read from the same strip in the same few seconds, so a strip held at an angle lets one run into the other and invents a gap that is not there.
Where to find it: Pool shops, hardware stores, supermarkets and online, sold both per parameter and as multi-packs. Buy strips made for your kind of water: pool strips and drinking water strips read very different scales for the same chemistry.
Digital photometer
- How trustworthy
- Dependable
- Cost
- Most expensive
- Effort
- A few minutes per parameter
The same reagents as a drop kit, read by an instrument instead of your eye. It removes the colour judgement and gives a repeatable number, which matters most for people who are colour blind or testing in poor light.
Reads both electronically off one sample, which removes the judgement call in the place it matters most — the two numbers are being subtracted, so an error in either goes straight into the answer.
Where to find it: Pool trade suppliers and water-testing suppliers online. Reagent tablets or sachets are an ongoing cost.
Free test at a pool shop
- How trustworthy
- Dependable
- Cost
- Free
- Effort
- A trip, and a sample carried carefully
Take a sample in and they will run it, usually on a photometer, usually free, and print you a full panel. The catch is that the printout ends in a list of things to buy.
A pool shop panel usually prints free and total side by side, which is a quick way to check whether your own kit's gap is real.
Where to find it: Most pool and spa retailers. Ask which parameters they cover before driving over.
Taking the sample
For several of these the sample is where the error is, and no instrument recovers from a bad one.
- • One sample, both readings. Two samples taken ten minutes apart are two different pools as far as this subtraction is concerned.
- • Elbow depth, away from the returns, with the pump having run. The same rule as free chlorine, and for the same reason.
Further reading: CDC: the Model Aquatic Health Code, the guidance US pool codes are written from
If it is too low
A total chlorine reading below your free chlorine reading is a measurement error rather than a finding: free chlorine is part of total by definition. Retest both on one sample, and suspect the free chlorine reading if the pool was shocked recently, since high chlorine can bleach a DPD test back to clear.
- • Nothing to do about this reading on its own. Read it against free chlorine.
- • If it genuinely comes back lower than free chlorine, replace the reagents before trusting either number — an old DPD powder pushes both readings the same way.
If it is too high
On its own this says nothing. Put it next to free chlorine: if the two are close together the chlorine in your pool is almost all still working, and if there is a wide gap between them, most of it is spent and the pool needs shocking rather than topping up.
- • Work out the gap: total minus free is combined chlorine. WiseWaterGauge does this for you when both are logged on the same test.
- • If the gap is wide, shock the pool to break the combined chlorine down. Topping up with more chlorine without shocking only adds to the same problem.
- • If the gap is small, there is nothing wrong. The total is high because the free chlorine is high, and that resolves on its own.
Common questions
Should I bother logging total chlorine if I already log free chlorine?
Yes, and it is the only reason this parameter exists. Free chlorine alone tells you whether the pool is sanitising now; total chlorine beside it tells you whether it is struggling to, which is the thing that arrives before a problem rather than after it.
My kit only gives me one chlorine number. Which one is it?
Almost always free chlorine — it is the number a swimmer's safety depends on, so it is what a basic kit is built around. If the instructions mention a second tablet, a second pad or a third reagent, that is the total chlorine test.
Why is there no safe range shown for total chlorine?
Because nobody publishes one. A pool can carry plenty of total chlorine and be perfectly well run, or carry the same amount and be full of chloramines. The published limit is on the difference, which is why this guide keeps sending you to combined chlorine.
WiseWaterGauge helps you record and understand your own readings. It is not a substitute for a certified laboratory test, and nothing here is medical or regulatory advice. If a health parameter is out of range, confirm it with an accredited lab and speak to your water provider.