What Causes Low Alkalinity In A Hot Tub?

Michael Keenan


Hot Tub Water Chemistry

Did you know that over 60 percent of hot tub owners face the issue of low alkalinity at some point or another? Having the right alkalinity level is very important for keeping the water balance and having a fantastic and safe soaking experience.

Low alkalinity can lead to several issues such as pH changes, wear and tear of equipment, and skin irritation. Learning what causes this problem is essential for every hot tub owner.

This article will explore the factors that lead to low alkalinity in a hot tub. I’ll discuss how total alkalinity has an effect on the water chemistry and what it does to your health and the lifespan of your hot tub components.

By the end of this article, you will have all the information you need to keep the proper alkalinity levels in your hot tub, making sure you have a clean, balanced, and delightful soaking experience.

what causes low alkalinity in hot tub

Understand Total Alkalinity

Total alkalinity is the measure of all the substances in your hot tub that can neutralize acids and help maintain a stable pH level, keeping your water crystal clear and inviting. Balancing pH is crucial for the overall effectiveness of your hot tub’s sanitizing chemicals.

The ideal alkalinity level is between 80 and 120 ppm (parts per million).

This article is part of a series of guides I have created to cover all aspects of managing hot tub alkalinity. You can use the main guide and then check out – how to raise alkalinity in your hot tub and how to lower alkalinity in a hot tub.

Everything you need to keep on top of it!

Causes of Low Alkalinity in a Hot Tub

Surprisingly, insufficient levels of alkaline substances in a hot tub can be attributed to various factors. The causes of low alkalinity in hot tubs are important to understand as it plays a major role in water chemistry. Here are some common reasons for low alkalinity:

  • Carbon Dioxide (CO2) Absorption: When CO2 dissolves into the water, it reduces the alkalinity levels.
  • Dilution: Adding fresh water or rainwater lowers the concentration of alkaline substances.
  • Rainwater Infiltration: Natural rainfall can introduce acidic elements that decrease alkalinity.
  • Water Replacement: Regular draining and refilling can dilute the alkaline components.

To raise the alkalinity in your hot tub, you can use specific chemicals like sodium bicarbonate or baking soda. These products effectively increase the overall pH level and restore proper alkalinity balance.

Next up I look at its potential consequences on both your health and hot tub equipment.

The Effects of Low Alkalinity

One potential consequence of insufficient alkaline substances in a hot tub is that it can negatively impact both your health and the equipment. Low alkalinity can lead to potential health risks for bathers, as it affects the tub water chemistry and balance.

When alkalinity is low, it can cause the pH levels to fluctuate, resulting in an environment that is not suitable for maintaining proper disinfection. It can seriously reduce the effectiveness of your sanitizer.

This creates a breeding ground for bacteria and other harmful microorganisms that can cause skin irritation, eye redness, and respiratory problems.

Low alkalinity can also damage the hot tub equipment over time. The corrosive nature of unbalanced water chemistry can deteriorate metal components such as pipes, heaters, and pumps.

So, maintaining appropriate alkalinity levels is crucial for bather comfort and preventing any long-term damage to your hot tub system.

Testing for Low Alkalinity

To ensure you’re aware of any potential issues with the alkaline levels in your hot tub, it’s important to regularly test the water chemistry using a specialized kit or spa test strips.

I recommend testing your hot tub water at least once a week – more if you are using it a lot or after any extreme weather for example. See my main guide on how to test your hot tub water like a pro!

Now let’s discuss how you can prevent low alkalinity without compromising the performance of your hot tub.

Preventing Low Alkalinity in Hot Tub Water

Keep your hot tub in tip-top shape by regularly monitoring and managing the alkaline levels to prevent potential pitfalls. To maintain proper alkalinity, follow these steps:

  • Test the water: Regularly check the alkalinity levels using a test kit to ensure they’re within the recommended range of 80-120 ppm.
  • If alkalinity is low, use an alkalinity increaser specifically designed for hot tubs. Follow the manufacturer’s instructions carefully. (baking soda and soda ash can work too).
  • Adjusting water chemistry requires precision. Add small amounts of increaser gradually until the desired alkaline level is reached.
  • Adjusting pH levels: After adding an alkalinity increaser, retest and adjust the pH levels if necessary. Use a pH increaser or decreaser to bring it back to the ideal range of 7.4 – 7.6.
  • Remember that other factors such as bather load and chemical usage can affect alkalinity.
  • Regular maintenance: Consistently monitor and adjust both alkalinity and pH levels to maintain a balanced environment for your hot tub.

By following these steps, you can ensure proper maintenance of your hot tub’s alkalinity levels and enjoy crystal-clear water all year round.

Frequently Asked Questions

How often should I test the alkalinity levels in my hot tub?

Regularly testing your hot tub’s alkalinity is essential to maintain the best water quality. It is recommended to check the levels every week and make sure they remain within the suggested range.

Can low alkalinity cause skin irritation or dryness?

Using a hot tub with low alkalinity can cause skin irritation and dryness. It can increase sensitivity, cause allergic reactions, and be uncomfortable.

Can low alkalinity in a hot tub affect the pH levels as well?

Low alkalinity can have a detrimental effect on pH levels. Alkalinity acts as a protector, preventing sudden changes to pH. It’s very important to keep alkalinity levels in check in order to ensure the tub is functioning properly. This is a key component of hot tub maintenance and water balance.


It’s no secret that low alkalinity in a hot tub can be a real bummer. It can cause all sorts of issues and leave your water looking and feeling dull. But don’t panic! You can still keep things in balance and make sure your hot tub stays the life of the party.

Regular testing, maintenance, and some tender loving care are key. So go ahead and enjoy your soak! Just remember to keep an eye on the alkalinity levels and make sure the good vibes stay alive.


michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years of experience in pool care, plant care, and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!