What Causes Low Alkalinity in Pools

When people ask me for advice on their swimming pools or spas on where they should start at the beginning of the season, I tell them that the most important critical parameter test to run for water treatment is the total alkalinity test because low or high alkalinity can make or break your pool water chemistry. What Causes Low Alkalinity in Pools?

  • Rain can be acidic
  • Increase in swimmer load
  • Topping your pool off with H2O that has low alkalinity-after backwashing/wasting
  • Chlorine-Chlorine is acidic
  • High H2O evaporation-losing H2O can dilute TA
  • Pool H2O agitation-H2O agitation increases loss of CO2 affecting TA
  • Lotions & detergents-Keep a pool shower

The pH and alkalinity of a pool are not the same measurements, but they are closely related. With alkalinity out of proper range, pH will become unstable keeping the disinfection product from doing its job.

What Causes Low Alkalinity in Pools


Proper Alkalinity and pH balance are key to maintaining a healthy pool or spa water.  Alkalinity helps to stabilize the pH balance in your pool. The alkalinity range for pools should be between 80 – 120 ppm, ideally at 100 ppm. The pH scale is 1-14, and the pool and spas should be between 7.2 – 7.6, ideally at 7.4.

They are both necessary but if the Alkalinity balance fluctuates too high or low range pH will follow and the pool water won’t be an Acid rain can cause alkalinity levels and pH levels to drop. Sweat and even urine may cause alkalinity levels to lower.

Low Acid pH Levels and Decrease Alkalinity in Pool Water


Causes of Falling Alkalinity

Alkalinity levels can decrease for a wide range of reasons, which extend to:

  • A high amount of rainwater enters the pool, which leads to the water’s TA being diluted
  • Acid rain can increase acidity levels and  cause alkalinity level and pH levels to drop
  • Sweat and even urine may cause alkalinity levels to lower (all those hineys can ruin your sparkling pool water)
  • If you happen to shock your pool with chlorine tablets, it’s important to understand that these tablets have low pH levels, which means that using too many chlorine tablets can lower alkalinity levels
  • High H2O evaporation-losing H2O can dilute alkalinity level 
  • Pool H2O agitation-H2O agitation from the filtration system increases the loss of CO2 affecting Total Alkalinity
  • Lotions & detergents-Keep a pool shower and demand that swimmers use it


Salt Water Pool Alkalinity Levels: Swimming Pool Lower pH Level


Salt chlorine generators are fairly new to the pool industry, and they are very useful and innovative for pool owners. What some pool owners may not be aware of when buying a salt chlorine generator is they actually increase your pool’s pH and Alkalinity. What exactly are pH and pool Alkalinity are.

How does salt water affect pH and alkalinity?  Much the same way it does in a chlorine pool.  Anything that enters your pool has a pH. That includes humans, animals, rain, dirt, leaves, bugs, and yes, salt.

Salt itself does not dramatically change the pH or total alkalinity in a swimming pool. However, the liquid form of chlorine generated by the salt cell will cause higher pH swings. This is very common during seasons when the source water is already high in alkalinity.

This poses a unique problem for saltwater pool owners: the challenge of constantly maintaining their pool pH.low alkalinity your pH levels can swing back and forth between being too high by natural causes such as evaporation or agitation of your pools’s water.

If you allow pH and alkalinity(TA) to rise without any response, it will result in water that could allow staining and scaling.  Salt pool owners who choose to perform no maintenance on their pool aside from adding salt usually find out in a couple of years they have to deal with major scaling problems, plaster staining, or unusual watercolors.

One of the simplest ways to avoid all these issues is to wash the generator cell with an acid wash a couple of times per summer season. This, on top of regular maintenance, should keep your pool running smoothly.

Total Alkalinity in Pools


Alkalinity is the buffer or stabilizer some people refer to as the “Muscle” for your pool or spa’s pH. Alkalinity is measured in parts per million (ppm). An ideal alkalinity range is between 80 – 120 ppm. If the Alkalinity is below 80 ppm, we recommend In The Swim Pool Alkalinity Increaser.

If your Alkalinity is above 120 ppm, In The Swim Pool pH reducer will do the trick. Alkalinity over 120 ppm may cause the water to cloud up and cause scale to form. Alkalinity under 80 ppm will cause the pH to move freely on its scale. This can damage the pool or equipment over time with corrosion.

Total alkalinity refers to the ability of the pool water to resist a change in pH. The key purpose total alkalinity serves is to help control the pH in the pool. It does this by acting as a buffer so that when materials are added to a pool that would otherwise cause the pH to go up or down, these changes are managed and do not result in severe changes to pool water balance.

Then you get the normal excess urine and perspiration in the pool water can play havoc with the pool water’s balance, swimming pool pH, and the water’s alkalinity, natural causes such as evaporation or agitation of your water pool water chemistry always changes. 

Warm pool water causes drastic changes in pool water pH especially during heavy loads on a hot day pH levels can drop right away 

When a foreign substance is added to the pool water that could affect the pH, total alkalinity will react to neutralize it and help keep the pH in the desired range. Total alkalinity does not determine what the pH will be but rather acts to help keep the pH in the range desired which is a balancing job the most important job in pool water treatment.

Pool spas, cement pools fiberglass pools, and reef pools all work the same with total alkalinity to help keep the pool’s water balance and clear pool clear.


Raise Alkalinity: Low Alkalinity in Your Pool


Do you need to raise pH without affecting alkalinity dropping Total Alkalinity? You can sometimes raise the pH by aerating the pool water. That’s right just add some air! It’s the same reason hot tubs and spas often suffer from high pH issues. Although this will bump your pH, it’s important to note that this isn’t an exact science, and results can vary by pool.

You can aerate a swimming pool by bubbling air through the pool water, agitating the surface, spraying droplets through the air with a pool fountain, or even get the kids just playing and splashing around in the pool. During the hot summer months, this method also can be used to lower pool water temperature.

Even the slightest alterations in pool water chemical composition can cause severe fluctuations in the pH levels. When the pH level becomes unbalanced, the phenomenon is called pH bounce and can cause low alkalinity in the pool.

With low alkalinity, the standard amount of chlorine added to your pool would be useless. It would only be useful when more than the usual amount is added for standard results. This means you buy more chlorine and waste more time and money trying to get to the right concentration level with the substance. Asides from its effects on your pool, a low-alkalinity swimming pool is unsafe for swimmers as the acidic water can cause nasal, eye, and skin rashes.


Is it Safe to Swim in a Pool with Low Alkalinity


Yes, but at the same time, the pool owner should find out the reason the alkalinity is low and adjust it right away. When the pool’s alkalinity is low, it becomes difficult to maintain the proper pH level for a safe, comfortable swimming environment. Thus, it’s essential to understand the causes of low alkalinity in your pool and how to correct it.

To raise the pool’s alkalinity safely, pool owners can use chemicals like sodium bicarbonate, also known as baking soda. This chemical can help balance the pool water by raising the alkalinity and buffering pH levels.

Pool owners should follow the instructions on the product label and test the pool water regularly to maintain the appropriate pool water balance.

Overall, it’s safe to swim in a pool with low alkalinity in the short term, but it’s essential to address the issue for the long-term health and safety of your pool and swimmers. Regularly testing your pool water and adjusting the alkalinity and pH levels accordingly helps maintain a safe, comfortable, and clean pool environment for swimmers to enjoy.

What causes High alkalinity in a pool?

  • Cyanuric acid also called CYA or chlorine stabilizer raises TA
  • Liquid chlorine (or ‘sodium hypochlorite) has a high pH
  • High Alkaline fill water
  • Soda ash-pH control
  • Sodium bicarbonate-pH control
  • TA rises due to excess hydroxides left behind ………………………………………. Read more


JimGalloway Author/Editor


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