Total alkalinity plays a huge role in your pool, but it can be confusing to wrap your head around when you’re first getting started.
This is a complete beginner’s guide to pool alkalinity, what it is, why it matters, how it works, and how to control it.
Quick answer: Alkalinity, or total alkalinity, measures your water’s ability to resist changes in pH, and it’s responsible for keeping your pH level stable. Aim to maintain a total alkalinity level of 80 to 120 parts per million (ppm).
What Is Total Alkalinity?
Pool alkalinity, total alkalinity, or simply TA, measures your water’s ability to resist change in the pH level.
This works by absorbing acids in the water, which prevents those acids from lowering your pH level. This is why total alkalinity is called a pH buffer, because it “shields” your pH from substances that would normally lower it.
To a lesser extent, total alkalinity also prevents sharp increases in your pH. The chemical process is a bit more complicated but it essentially involves taking up resources in the water that are required for pH to rise.
In short, the higher your total alkalinity, the more stable your pH level will be, and the harder it will be to adjust.
Why is Total Alkalinity Important?
Total alkalinity matters because your pH level matters.
The ideal pH level for your pool water is slightly basic at somewhere between 7.2 to 7.8. This is where chlorine works best without making the water too harsh on your skin, hair, and eyes.
Keeping your pH level within this range is extremely difficult without total alkalinity keeping guard, as it provides a buffer to counteract small changes in the water chemistry.
Without it, your pH could fall too low, causing the water to become corrosive to your pool surfaces and equipment, including the etching of plaster. It may also drift too high, leading to calcium scaling.
What Makes Up Your Total Alkalinity?
There’s a lot of “stuff” dissolved in your pool water. Some of that stuff absorbs acids like a sponge, and those substances make up your total alkalinity.
These mostly include carbonates, bicarbonates, hydroxides, and cyanurates, which are often introduced to the water through products that help you adjust pH and alkalinity, as well as chlorine stabilizers.
For example, every time you raise your pH level with soda ash, you introduce more carbonates to the water, and every time you use stabilized chlorine tablets, you introduce more cyanurates to the water.
Perhaps the best example, though, is baking soda. This is used to directly increase alkalinity by adding more bicarbonates to the water.
Note: A common misconception is that all alkaline substances in the water contribute to total alkalinity. However, it only includes alkaline substances that are able to absorb acid, such as those listed above.
How is Total Alkalinity Different from pH?
It’s easy to confuse pH and total alkalinity because “alkaline” is a measurement on the pH scale, but they’re not the same thing.
When you measure pH, you’re looking at how acidic the water is based on how much (or how little) acid is dissolved in your water. This is represented on the pH scale from 1 to 14.
When you measure total alkalinity, you’re basically looking at how effective your water is at negating acid before it has a chance to influence your pH level. This is represented in parts per million or ppm.
If you imagine pH as a battery, total alkalinity is like a surge protector, absorbing electrical spikes that would otherwise wreak havoc on the battery.
How Does Total Alkalinity Influence pH?
Total alkalinity has a strong influence over pH, so they do often correlate.
When your total alkalinity is very high, your pH level becomes very resistant to changes in the water, particularly the addition of acids that would normally lower it. As a result, the pH tends to drift upwards over time.
The same is true in reverse. When your total alkalinity is very low, any acid introduced to your water will significantly lower your pH because it doesn’t have the buffer it needs to resist that change.
With that being said, they are still different measurements and they can still act independently of one another, which means it’s not impossible to see a pool with high pH and low alkalinity, or vice-versa.
What is the Ideal Alkalinity Level?
The ideal level for total alkalinity in a swimming pool is between 80 and 120 parts per million (ppm). This provides enough of a buffer to your pH without making it too difficult to adjust when you really need to.
However, all pools have a sort of “resting pH” the water tries to get back to, and this can sometimes be on the very edge of the ideal pH range (7.2-7.8). In that case, adjusting the total alkalinity to compensate is a good idea.
For example, if your pH level tends to sit at around 7.8, you may need to reduce your total alkalinity below the 80 ppm threshold. This will free up more acid in the water and keep your pH from rising so easily.
Saltwater pools also require a slightly lower level, often somewhere between 50-80 ppm, because you have to account for conditions inside the salt cell where scale formation is more likely to occur.
What Causes Total Alkalinity to Change?
A lot of things can change your pool’s total alkalinity.
Some of these things directly increase your total alkalinity, such as adding an alkalinity increaser (baking soda), pH increaser (soda ash), or even chlorine stabilizer (cyanuric acid).
Adding any kind of acid to your water will eat through your pH buffer, which reduces your total alkalinity. Many types of chlorine are acidic, as is muriatic acid and sodium bisulfate (dry acid).
Other things are more indirect, such as when chlorine interacts with organic contaminants in the water (sweat, urine, sunscreen, leaves, insects, etc.), creating an acid byproduct that will also lower your total alkalinity.
Let’s not forget rainwater, which can dilute the water and therefore lower the concentration of total alkalinity. The same applies if you drain and refill the pool, depending on the total alkalinity of the fill water used.
The opposite is true for evaporation, which slowly increases your alkalinity as your pool loses water, although this effect is much more subtle.
How Do You Test Total Alkalinity?
Most pool testing kits allow you to test your total alkalinity, along with pH, free chlorine, calcium hardness, and cyanuric acid.
Test strips are more widely used because they’re easier, faster, and cheaper than other testing methods.
A strip is simply dipped into your pool water, causing it to change color based on your total alkalinity. The color is then measured against the provided chart to determine a rough level.
Liquid testing kits are considerably more accurate, though require a bit more patience and a bigger upfront investment.
These also rely on a color chart to determine a level, but the testing process uses a method called titration. It requires filling up a vial with water from your pool before adding drops from a reagent bottle.
Note: If you’re still unsure about which type of test kit to use, we wrote an article comparing both testing methods.
How Do You Adjust Total Alkalinity?
If your total alkalinity isn’t where it needs to be (typically between 80 and 120 parts per million), you’ll need to adjust it.
When total alkalinity is too low, you need to add more of those acid-absorbing substances to the water in order to raise alkalinity.
The most effective and easiest to control, at least in terms of raising your total alkalinity, is bicarbonate. You can add bicarbonates to your water by simply adding sodium bicarbonate (baking soda).
Adding sodium carbonate is another common way to increase alkalinity in a pool, but carbonates will simultaneously raise your pH level. This can be useful if both your total alkalinity and pH are low.
When total alkalinity is high, you need an acid to eat away at your pH buffer, thereby lowering your total alkalinity.
While any acid will work, muriatic acid (hydrochloric acid) is very effective, widely available, and inexpensive, which is why it’s often seen as the most practical choice for most pool owners.
If safety and handling are more of a concern, sodium bisulfate (dry acid) is another popular option. Unlike muriatic acid, dry acid comes in granular form and doesn’t give off harsh fumes.
How Do You Maintain Total Alkalinity?
Total alkalinity works hard to stabilize your pH level, but there isn’t anything in the water doing the same for your total alkalinity.
That means your total alkalinity will fluctuate.
The only way to manage this is by sticking to a robust pool maintenance schedule that includes regular testing, and always having the right substances on hand to adjust your total alkalinity as needed.
You’ll also need to respond quickly to external factors, such as heavy rain, that will likely throw your total alkalinity out of balance — but this applies to all facets of pool chemistry, not just alkalinity.
Finally, if staying on top of your total alkalinity (or even your pH level, chlorine level, etc.), consider hiring a pool guy to handle it all for you.
The Bottom Line
Total alkalinity is a buffer that keeps your pH level stable by absorbing acid content in the water. This allows you to keep your pH at the most optimal level for proper sanitation and a comfortable swim.
For most pools, keeping total alkalinity between 80 and 120 parts per million will give you the best results, and this can be achieved through regular testing and substances like baking soda and muriatic acid to adjust as needed.