Total Alkalinity
The water's resistance to pH change. Get this right and pH stops fighting you.
- Safe range
- 60 – 180 mg/L
- Ideal range
- 80 – 120 mg/L
- Measured in
- mg/L
What it is
Total alkalinity measures the water's capacity to absorb acid without its pH moving, its buffering ability. It is not the same as pH. Think of pH as where the water currently sits and alkalinity as how hard it is to push it somewhere else.
Why it matters
Alkalinity is why pH either behaves or does not. With alkalinity too low, pH swings wildly on small inputs: a rainstorm or a dose of acid sends it somewhere unhelpful, a condition often called pH bounce. With it too high, pH becomes stubborn and drifts upward no matter what you add. Chasing an unstable pH without fixing alkalinity is the most common wasted effort in pool care.
How to measure it
A drop-count titration kit, and nothing else is really worth buying. This is the parameter where counting drops beats matching colours by the widest margin, and it is the one you are meant to get right first.
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.
Reagent goes in a drop at a time until the sample changes colour, and the number of drops, multiplied by whatever your kit's instructions say, is the answer. There is no shade to grade: only a change to notice.
Watch out: Hold the reagent bottle vertical and squeeze slowly. A bottle held at an angle makes smaller drops, and since the count is the answer, that error goes straight into the number.
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.
Alkalinity is one of the better pads on a strip, and fine for spotting a large drift between proper tests.
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.
Included in any pool photometer's panel, and the reading needs neither drop counting nor arithmetic.
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.
Always on the printout, and a sensible cross-check at the start of a season before you begin dosing on your own numbers.
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.
- • Test alkalinity before pH, and read a pH that will not stay put as a question about this number rather than about pH.
- • Retest a full circulation cycle after adding bicarbonate. Alkalinity adjustments look like they have done nothing for the first hour.
If it is too low
pH will not hold steady, swinging on small additions or after rain. The water also becomes more aggressive toward plaster, grout and metal.
- • Add sodium bicarbonate (baking soda), which raises alkalinity with relatively little effect on pH.
- • Work in stages and retest; large single doses tend to overshoot.
If it is too high
pH becomes hard to lower and tends to creep upward. Often brings cloudy water and scale, and makes every other adjustment feel unresponsive.
- • Add acid to lower it, then aerate the water to bring pH back up while alkalinity stays down.
- • Expect this to take several rounds. Lowering alkalinity without dragging pH with it is inherently fiddly.
Common questions
What is the difference between pH and total alkalinity?
pH is how acidic or basic the water is right now. Total alkalinity is how strongly the water resists changing that. You can have correct pH with bad alkalinity, and it will not stay correct for long.
Why does my pool pH keep changing?
Almost always low total alkalinity. Without enough buffering, rain, swimmers and chemical doses each move pH significantly. Bring alkalinity into its own target range — the figures are on the Total Alkalinity guide — and pH usually settles on its own.
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.