High Alkalinity

High Alkalinity In Pool - How To Reduce It?

The total alkalinity of your pool acts as a buffer to maintain balanced pH levels in your water, but what happens when these levels get too high? High alkalinity can cause problems for your pool that affect its structural integrity, water chemistry and even the comfort of your swimmers.

In this article, we will discuss the ideal levels of total alkalinity that you should have in your pool, how to test your pool’s levels, and the potential causes of high alkalinity. We also cover the problems associated with high alkalinity, how to decrease your levels, and how to prevent alkalinity from becoming too high in the future.

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Ideal Total Alkalinity Levels In Pools

The total alkalinity in your pool works to stabilise the pH of your water. Some fluctuation in your pool’s pH levels is a normal occurrence, and total alkalinity works to help maintain balance when pH levels are disrupted.

The ideal levels of total alkalinity in your pool range from 80-120 parts per million (ppm). Alkalinity adjustments do not necessarily need to be made if your pool’s levels fall within this range, unless they are tending to run high.

If your pool’s total alkalinity levels are higher than 120ppm, you will need to take steps to reduce your alkalinity to prevent unwanted side effects for your pool’s equipment and swimmers.

This tends to be less common than the reverse problem, which is low pool alkalinity.

Causes of High Alkalinity

High alkalinity can be caused by an overuse or repeated application of chemical treatments is a very common cause of high alkalinity.

Alkalinity is also increased by skincare products and similar substances entering the pools, such as sunscreen, moisturisers, or hair products.

Occasionally, high alkalinity can also be caused by an overuse of alkaline raising products, typically caused by using an incorrect dose for your pool, or by adding more before your original dose has dissolved in your pool and properly circulated.

Problems Associated With High Alkalinity

High alkalinity can cause many problems for your pool, including increasing the likelihood of metal stains and hard water scaling caused by calcium. It can also cause your pool water to turn cloudy or become unsanitary.

High alkalinity levels and the high pH that often accompanies them will also cause your chlorine to lose effectiveness as a disinfectant (particularly for unstabilised chlorine), allowing microscopic organisms such as algae and bacteria to flourish and reproduce.

Water with a high alkalinity also causes sensitivity and burning in the eyes and nose, and may cause skin irritation that lasts for hours after getting out of the pool.

High alkalinity may also damage swimming equipment such as goggles and pool toys by causing elements of the plastic and rubber components to degrade faster.

Pool machinery can also sustain significant damage if adequate total alkalinity levels are not maintained, and a subsequent buildup of calcium scale can stiffen moving parts such as those in your filter housing, pump unit, or skimmer basket.

Diagnosing High Alkalinity

In order to figure out the level of total alkalinity in your pool, you will need to test your water with an adequate test kit. Most testing kits for pool chemistry contain testing solutions for total alkalinity. Solution-based test kits allow for the most precision when testing water chemistry.

We recommend test kits that employ testing solutions in order to get the most accurate results, but there are other options available. Solution-based water chemistry test kits can be time consuming and leave more room for user error.

Most 4 in 1 Test Strips also test for total alkalinity, and makes a great option for pool owners seeking a test kit that can evaluate all of their pool’s chemistry at once.

How to Decrease Pool Alkalinity

In order to decrease pool alkalinity you will need to use products known as dry acids. Dry acids are often sold in pool supply stores as pH decreasers, but pH and alkalinity are linked, so lowering alkalinity will also lower pH. The most common compound sold for this purpose is sodium bisulphate, which reduces alkalinity and pH.

Dry, powdered products like sodium bisulphate are much safer to handle than concentrated liquid acids and easier to store and manage.

It is important to make sure you use the correct dosage for your pool’s volume according to the instructions provided on your product’s packaging. Most products containing sodium bisulphate can be used in the same ratio: 375 grams of product can reduce the total alkalinity in a pool of 25,000 litres by 10 ppm.

Many products require mixing in a bucket of pool water that is then supposed to be dispersed around the perimeter of your pool. When mixing chemicals such as alkalinity in a bucket, it is crucial to add water to the bucket before adding your chemicals. We recommend using pool water, but fresh water from your tap can also be used.

Mixing these products carefully according to instructions will prevent a highly concentrated acid from being produced, which can be dangerous if it comes in contact with your skin or eyes. A chemical reaction with the incorrect ratio of product to water can also produce unhealthy fumes.

Once you have produced your mix with care, it should be introduced to the pool while the pump is running, and the pump should be left on for a minimum of two hours after treatment to ensure proper circulation.

After your pump has been run for a minimum of two hours, or ideally 3-4, you will want to retest your pool’s total alkalinity levels and decide if another dose is needed. Always follow package instructions to ensure proper dosing in relation to your pool’s volume to avoid overuse of products or ineffective treatments.

Preventing High Alkalinity in the Future

In order to prevent high alkalinity in the future, it is helpful to determine what caused your levels to rise. If your high levels of total alkalinity were caused by an overuse of chemicals such as shock treatments or pH increases, it’s important to ensure that a correct dose is used next time you treat your pool.

High alkaline caused by a salt chlorine generator builds up slowly over time, and is harder to prevent. It is also inevitable that skin and hair care products will come in contact with your pool water unless you ask your swimmers to shower before entering the pool.

In these cases, it may be necessary to add small doses of sodium bisulphate or another alkalinity decreasing chemical to your water on a regular basis.


High alkalinity can lead to other problems with your pool’s chemistry including high pH. It also increases the amount of potential staining and scale buildup, which often damages pool equipment and machinery.

Although high alkalinity has detrimental effects, it is a fairly easy problem to resolve. Pool chemicals known as alkalinity decreasers, often containing sodium bisulphate, can be carefully mixed and then added to your pool’s water to achieve drastic results.

High levels of alkaline are not always preventable in a pool, as many things naturally cause your alkalinity levels to increase. Because of this, keeping an alkaline decreasing product in your pool supply cabinet is the best defence against high levels.

Do you have any questions about decreasing high alkalinity levels in your pool? Leave us a comment down below, we would love to help!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.