Balancing pH & Alkalinity in a Hot Tub: A Troubleshooting Guide

pH and alkalinity are both important in maintaining the proper water chemistry in your hot tub. The pH level refers to the acidity or basicity of the water, and is measured on a scale of 0 to 14. Total alkalinity (or TA) refers to the water's ability to resist changes in pH, and is measured in parts per million (ppm).

The ideal pH level for a hot tub is between 7.2 and 7.8. It's critical to maintain the proper pH level because if it's too low, it can cause skin irritation and corrosion to the hot tub's components. If the pH level is too high on the other hand, it can also cause skin irritation—and make your sanitizer less effective.

Alkalinity is also important because it acts as a buffer to keep the pH level stable. If the alkalinity is too high or low, the pH level can change quickly and become difficult to control. The alkalinity level for a hot tub should be somewhere between 80 and 140 ppm in most cases.

What causes high pH in a hot tub?

A high total alkalinity (TA) is the most common reason for the pH level to rise in a hot tub. When the TA is too high, it means there are too many alkaline substances in the water, which makes it more difficult to lower the pH level. In addition to high TA, here are a few other possible causes of high pH in a hot tub:

• Overuse of pH increasers: Certain chemicals can be used to raise the pH level in a hot tub. If too much is added, it can cause the pH level to get out of control.
• High levels of calcium or magnesium: These minerals can naturally occur in the water supply or be added after, and can contribute to high pH levels.
• Organic material: Contaminants such as sweat, oils, and lotions can also contribute to high pH levels.
• Improper water balance: If the water balance (pH, TA, and calcium hardness) is not maintained overall, it can cause pH levels to fluctuate.

It's important to regularly test the pH level in a hot tub and make adjustments as needed to keep it within the desired range. If you are unable to lower the pH level despite adjusting the TA, you may need to drain and refill the hot tub with fresh water. Sometimes it's better to just start over.

What causes high alkalinity in a hot tub?

The most common cause of high TA is simply regular use of the hot tub! Why? Well, when you use the spa, the aeration from the jets, along with the high water temperature, accelerates the outgassing of carbon dioxide from the water. So, when the water is agitated by the jets and heated, it releases carbon dioxide.
This raises the overall total alkalinity.

Over time, if this is not corrected, a high TA level can make it difficult to bring the pH back down the proper level, even with the right chemicals. It's important to test the water regularly, and adjust the alkalinity as needed, to prevent this from happening.

Why does my hot tub pH keep dropping?

There are a few reasons why the pH level in a hot tub may be dropping:

• Heavy hot tub usage: Again, hot tub usage can also cause the pH level to drop due to contaminants such as sweat, oils, and lotions that are added to the water by bathers. These contaminants can lower the pH level.
• Acidic sanitizer: Some types of sanitizers, such as bromine or trichlor chlorine tablets, are naturally acidic and can therefore lower the pH level over time.
• Low total alkalinity: Total alkalinity acts as a buffer to help keep the pH level stable, so if the TA is too low, it can make it difficult to maintain a consistent pH level, and the pH level can drop as a result.

Why does my hot tub alkalinity keep dropping?

The reasons for total alkalinity in a hot tub dropping are quite similar to the reasons for a low pH:

• Bromine sanitizer: As I mentioned, using bromine sanitizer can cause the TA level to drop because bromine is an acidic chemical and therefore can lower the alkalinity level.
• Acidic sources of chlorine: Other types of acidic sanitizers, such as trichlor, can also lower the TA level. This is why it's not generally recommended to use chlorine tablets in a hot tub.
• Not enough aeration: If you're an infrequent spa user, or you prefer to use it without the jets, you won't be getting the TA-raising benefits of aeration. Try running the jets for frequently to see if it helps.

Of course, it's important to note that you should still regularly test the water for pH and TA and make sure the pH is staying in range. If you are unable to keep it stable despite adding borates, you may need to add baking soda more frequently.

How to lower pH without lowering alkalinity

Lowering the pH level without lowering alkalinity is actually very difficult, so it usually involves a two-step process. Here are the steps to follow:

1. First, you need to add a pH down product, also known as pH decreaser (all basically types of acid). After adding the pH down, test the pH level again to ensure it has been lowered to the desired level.
2. Next, you need to raise the alkalinity, typically with baking soda or sodium bicarbonate. Then, test both the alkalinity and pH levels again to check they're both in range.

Keep in mind that adjusting the pH and alkalinity levels is a balancing act, so you may need to repeat this process a couple of times.

How to lower alkalinity without lowering pH

In most cases, it's actually not necessary to lower the alkalinity in this situation. If the pH level is within the desired range, it's best to just leave the alkalinity as it is.

Remember that the purpose of TA is simply to stabilize the pH, and for some spas, this might fall outside of the generally recommend range. If your pH is happy, all is good!

How to raise pH without raising alkalinity

The only way to raise the pH level without raising alkalinity at all is through aeration. This can be achieved by turning up the jets on your hot tub, which will create more surface agitation, which in turn will release carbon dioxide and raise the pH level. The TA will remain the same. However, this method may not be very effective or consistent, as it relies on how frequently you're able to use the spa.

Another method is to add a pH increaser such as sodium carbonate (also known as soda ash) or 20 Mule Team Borax:

pH Increaser for Pools, spa, Hot Tub - Granular 100% Sodium Carbonate (Soda Ash) to Raise pH Up, 10 lb

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Both will raise the pH level, but will also raise TA (at least a little).

After 30 minutes, you should re-test to make sure the pH has been raised to at least 7.2.

How to raise alkalinity without raising pH

The most common method to raise the TA is to add an alkalinity increaser such as sodium bicarbonate, also known as baking soda. This will raise the alkalinity level without significantly raising the pH level.

Although a small pH increase will usually still occur, it should be minimal compared to the TA increase you will gain.

Final thoughts

In summary, pH and alkalinity are both important factors in maintaining balanced water chemistry in a hot tub. They are related in that pH level affects the safety and cleanliness of the water, and alkalinity helps to stabilize the pH level.

Changing one is often difficult without affecting the other, so make sure you have the right chemicals on hand, and an understanding of how these two measurements interact with each other.