What is Alkalinity in a Pool and Why is It Important?

The alkalinity is an important part of water treatment in swimming pools. But what exactly is the total alkalinity, and how should the ideal alkalinity parameter look like?

In the pool, the alkalinity (total alkalinity or TA value) describes the buffer capacity of the pool water against acid entry. The alkalinity in the pool should be between 80 and 120 ppm. For better optimization, the water is measured in ppm using the photometric method.

I explain everything about alkalinity (acid capacity) in this article, how to maintain the total alkalinity in the pool and what resources you need to measure and optimize the parameters.

What does alkalinity do for a pool?

The alkalinity is also referred to as acid-binding capacity, acid capacity – don’t let that fool you.

The total alkalinity in your swimming pool describes the buffer capacity of the pool water.

This means that the pH level in your swimming pool or whirlpool remains stable against the entry of acids – e.g., from rain, since rain is always acidic.

In the USA, it is assumed that total alkalinity (term in the USA instead of acid capacity) indicates the concentration of minerals in the water.

In short: the alkalinity is crucial for pool maintenance and must be kept in balance.

This works best with regular measurement of the pool water – I recommend the following water tester.

Exact measurement results are important for optimizing the alkalinity.

But what does the acid capacity KS 4.3 mean, for example?

The acid capacity is calculated using the formula:

KS4.3 [mmol / l] = V * c * 1000 ml sample volume

Don’t worry.

As a pool owner, you don’t have to calculate big – the acid capacity KS 4.3 tells you how much acid has to be added to the pool in order to reach the pH level of 4.3.

Too complicated?

I’ll explain to you in my blog – even without the Nobel Prize in Chemistry – how you can reduce or increase the alkalinity in the pool.

Just click the links to see the articles.

In the next chapter, I explain how to measure the alkalinity in the pool.

How is the alkalinity measured in the pool?

Even for experienced pool attendants, it is not always easy to identify the acid capacity as the main cause of various problems in the pool.

Beginners, in particular, make a lot of mistakes when optimizing alkalinity, which in turn leads to poor pH.

You can probably guess the rest of the story.

However, this is often only due to the fact that the acid capacity – such as the pH value or the free chlorine – is measured with simple test strips.

The water test strips are not accurate when it comes to determining the alkalinity in the pool.

A much more effective method is the photometric or titrimetric method. I recommend the following water tester.

The acid capacity in the pool can be corrected based on the measured values.

How high does the alkalinity have to be in the pool water?

In the USA, a value between 100 and 150 ppm is recommended.

But from my own experience, an alkalinity in the range between 80 and 120 ppm is optimal for private swimming pools.

Setpoints of the alkalinity in the pool:

0.8 to 1.2 mmol/l = 80 to 120 ppm = 80 to 120 mg/l = 4.48 to 6.72 °dH

Unit mmol/l ppm mg/l °dH
1 mmol/l 1 50 50 2,8
1 ppm 0,02 1 1 0,056
1 mg/l 0,02 1 1 0,056
1° dH 2,8 17,9 17,9 1

Using the table shown, you can easily convert the alkalinity into other units, depending on the measuring device.

List of abbreviations:

  • mmol/l: millimoles per liter
  • mg/l: milligrams per liter
  • ppm: Parts Per Million 10-6
  • °dH: Degree of German hardness

It is enough that the acid capacity in the pool is measured once a month.

If the number of bathers and the frequency of use of the pool increases, measurements must be taken more often than once a month.

Tip: I recommend measuring the acid capacity in the pool, especially after a storm.

In the further course of the text, I describe the effect of the alkalinity on the pH value and calcium hardness.

Interaction between pH and acid capacity

The alkalinity is related to the pH value and consequently also to the calcium hardness.

If you’ve already read my article on pool chemistry, then you know that these three parameters are critical to water balance in the pool.

This means: If the alkalinity in the whirlpool or pool is not at the optimum at 80 – 120 ppm, then the pH value and the calcium hardness fluctuate – the pool water quickly turns green and cloudy.

That is why the alkalinity must be checked regularly in addition to the pH value.

If you notice strong fluctuations in the pH value, I recommend measuring the alkalinity and, if necessary, correcting it first before bringing the pH value to 7.2 – 7.6.

But is a fluctuating pH in the pool the only problem with an incorrect TA?

In the further course of the text, the consequences and possible problems in the pool are described if the alkalinity is neglected.

Reasons why the alkalinity rises and falls

I have often seen laypeople desperate because of mustard algae and other pool cleaning problems.

A lot of money was wasted on pool chemicals and the continuous operation of the pool pump. All because one has neglected the effect of the alkalinity in the pool.

But what are the reasons that the pool alkalinity increases?

  • Bathing habits: No shower before entering the pool.
  • Water temperature: High temperatures cause the alkalinity in the pool to rise.
  • Pool pump: The turbulence caused by bathers and the continuous operation of the pool pump increases the total alkalinity.

Read my blog about what to do if the alkalinity in the pool is too high.

Why is the alkalinity dropping in the pool?

  • Acid entry: If there is too much acid – e.g., from rainwater – in the pool, the alkalinity drops below 80 ppm.
  • Too much cyanuric acid: Excessive use of cyanuric acid will lower the total alkalinity.

Read in my blog what to do if the alkalinity in the pool is too low.

I will explain the exact consequences of a deviation in alkalinity from the ideal value in the next chapter.

Damage from poor alkalinity in your pool

Is poorly optimized total alkalinity in the pool really that bad?

The total alkalinity only influences the pH level, and what can go wrong, except that the pool water turns green?

It is true that acid capacity affects pH, but the consequences of incorrect TA and pH levels ​​are not just green or milky pool water.

  • If the pH is below 7, the water is acidic and corrosive. Metal parts in the pool start to rust, and the limescale is loosened from the joints.
  • Damaged joints are ideal nesting places for blue algae (black algae), which are dangerous for humans. That, in turn, means expensive renovation work on the pool basin.
  • If the pH level is too low, disinfectants are used up faster – there are extra costs for pool maintenance.
  • High alkalinity and the associated high pH level above 7.6 leads to calcium in the swimming pool – fogged up walls, limescale rim in the pool, and calcified filter sand.
  • If the alkalinity is above 120 ppm, foam often forms in the pool.
  • Redox voltage is difficult to calibrate if the alkalinity is incorrect.

I repeat myself: the monthly measurement of the alkalinity in the pool should not be neglected.

Do you have any other questions about pool alkalinity?

Contact me at @contactswimfool on Facebook, Twitter, Pinterest, and other popular social media. I am happy to help you.

Have fun optimizing the alkalinity.

Photo of author
Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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