How to Lower Alkalinity in Hot Tub: 3 Tested Methods

Hot tubs are wonderful and relaxing but they need to be maintained to keep them this way. If you don’t regularly test and adjust the water it can cause skin irritation, cloudiness and problems with scale. Once you know how to keep the water in a hot tub within the right levels you can sit back and enjoy your spa. 

If you need lower alkalinity levels in a hot tub, you first need to test the water and measure out pH decreaser or hot-tub approved acids such as sodium bisulfate or muriatic acid. Circulate the water for 30 – 60 minutes before testing the alkalinity again. 

How to Reduce Alkalinity in Hot Tub 

Fortunately, reducing the alkalinity of a hot tub is straightforward. There are a few different ways to do this.

1. Add pH Decreaser 

You probably have a pH decreaser as part of the spa maintenance kit. Test the water and add the appropriate amount of pH decreaser. Wait for 24 hours and then retest the water. Although pH and alkalinity are different, decreasing the pH usually works to decrease the alkalinity too.

2. Add Sodium Bisulfate

This is a dry acid that can be added to the water to reduce the alkalinity. Before adding sodium bisulfate, test the water so you know the total alkalinity. Then, measure the amount of sodium bisulfate needed and mix this with a bucketful of water from the tub. Stir this until the dry acid has completely dissolved. You can then add the bucket of water back into the tub. Once the water has had time to circulate, retest the alkalinity.

3. Add Muriatic Acid 

Another type of acid you can use in hot tubs is muriatic acid. Handle this with care as it can irritate skin. Before adding muriatic acid, turn the hot tub pump off. Then test the water and follow the muriatic acid directions to calculate how much is needed. Add the measured amount to a bucket of water taken directly from the tub and mix well. Add the water back into the tub and wait 60 minutes before turning the pump back on and retesting the alkalinity of the spa.

How to Lower Alkalinity in Hot Tub Without Affecting pH

Maintaining water in a spa can be a balancing act at times. Below we discuss how to lower the total alkalinity without impacting the pH by using aeration.

Step 1. Turn on the Jets 

You want to aerate the water so turn on the air and jet features on the hot tub. Leave them on while you work your way through these steps. The jets play an important role in helping to maintain the pH level while you lower the total alkalinity of the tub.

Step 2. Test the Water

You need to calculate how much you need to reduce the total alkalinity. To do this, test the water to get an alkalinity reading. Then, use this to calculate how much acid you need to add to the water. The amount will depend on the size of the hot tub, the alkalinity reading and the chosen acid.

Step 3. Add Half the Acid

Now add half of the amount of acid you need to add into a bucket of tub water. Stir until it dissolves and then add the mix to the tub. Always add the acid into the water and not the other way around.

Step 4. Leave for Half an Hour

After adding 50% of the acid, leave the hot tub for half an hour. Make sure you leave the jets on to continue to aerate the water. You are only adding half of the necessary amount because we want to reduce the alkalinity slowly without impacting the pH level. Having the jets on can also help to move the acid around so the water fully absorbs it.

Step 5. Test the Water

After 30 minutes, test the water. If the total alkalinity is still lower than the target and the pH is more than 7.8 then calculate the amount of acid needed to bring the alkalinity down and repeat steps 3 – 5.  In a situation where the total alkalinity is lower than the target but the pH is more than 7.6, leave the hot tub to aerate for a further 30 minutes before testing again.

Step 6. Continue Until You Reach the Target Alkalinity 

Work your way through the steps from step 2 onwards until you reach the target total alkalinity. Each time the acid you add should be less and less as this allows you to lower the alkalinity within a couple of hours. With each test the pH level should remain more or less the same.

Understanding pH and Alkalinity 

The water alkalinity of a hot tub is a measure of the hot tubs ability to neutralize acids. The alkalinity plays a role in the balance of the pH level and helps to prevent big changes in pH. The pH is how much hydrogen ion is in the water and is measured from 0 – 7. 0 Neutral is 7 and anything higher than this is alkaline or basic while anything lower than 7 is more acidic. You can think of the alkalinity of the hot tub as a natural protection against acids. 

If the level of alkalinity is too high or too low then it can be harmful. This is why it is important to maintain the alkalinity and test the water regularly. When you adjust the alkalinity it will also impact the pH level so don’t forget to test both levels. Low alkalinity is more likely to cause large pH fluctuations. 

What Causes High Alkalinity in Hot Tub?

Knowing the cause of high alkalinity can help you deal with it. Once you know why the water alkalinity is high it is easier to lower it.  

1. Lotions & Care Products

A potential factor that can impact the water quality and levels is the products bathers have on their skin and hair. That’s right, the lotion and body care products used by the people in the water can impact the alkalinity. Sunblock, perfume, shampoo, hair products and body lotion can all contribute to the changes. Rinsing these products off before getting into a hot tub can help prevent the alkalinity and pH levels from being affected.

2. Other Pollutants

In addition to products and body oils, the alkalinity can be the result of debris, leaves and even food. Anything that the bathers could bring into the tub on their body can impact the water’s total alkalinity. 

3. Too Much Alkaline Increaser

Adding too much alkaline increaser than the tub needs will result in high alkalinity. It’s more common to need to increase alkalinity than decrease it, so adding increasers is relatively common. Simply over measuring the amount you need can be the cause of the problem. 

4. Chemicals

Maintaining a hot tub requires chemicals and this could be the reason the total alkalinity level has increased. Using too many different chemicals can cause an increase in the total dissolved solids which in turn causes a high alkalinity level. To prevent this from being a problem in the future, don’t mix chemicals. Mixing chemicals won’t only alter the pH and alkalinity levels of the tub water, it can also be dangerous for your health.

5. High Alkaline Water 

If the tap water you used has a high level of alkalinity then this is the cause of the issue. Test the water you are using to determine if this is why you are getting high alkalinity readings. A hose filter can help to control the water going into a hot tub. The filter helps to stop solids and contaminants, giving more control over the overall alkalinity level. 

Issues With the Filtration System 

If the filtration system is damaged or not functioning as it should then this can cause the alkalinity levels of the spa to be high. Check the filtration system and replace it if needed. The filtration system plays an important role in the tub so it needs to be maintained and functioning at all times. 

What Happens in Alkalinity is Too High in Hot Tub 

If the total alkalinity is too high then you may be able to notice it visually. There are a number of things that happen which is why it’s important to lower the alkalinity as soon as you realize it is too high.

Build Up of Scale 

High alkalinity means there is also an increase in calcium. More calcium in the tub results in more scale, this can often be seen on the surface of the tub’s water. The increase in calcium can also cause a build up in the system which can damage the equipment. If the water regularly tests as high alkalinity then it is worth checking the health of the spa system and making sure the jets aren’t clogged. 

Ineffective Chlorine 

A high alkalinity level causes a higher pH level and this makes the chlorine less effective. Chlorine is used to sanitize the water and keep it clean. If the chlorine cannot do its job then the water will become higher in bacteria, contaminants and algae. 


You may notice the water looks cloudier than usual. Cloudy water is the result of the increased calcium levels. Cloudiness in the water is a visual indicator that the total alkalinity levels are too high.

Higher Levels of Irritation for Bathers

Too much alkalinity in the water can cause stinging eyes as well as irritation of the skin and nose. It may also cause swimsuit fabrics to fade. 

Higher pH Levels

As mentioned, high alkalinity causes high pH levels. Therefore, when you balance the alkalinity you also need to test and balance the pH. 

Related Questions

Dealing with alkalinity and pH can be confusing, to help make this easier we’ve answered common questions below.

Will pH Decreaser lower alkalinity?

Yes, pH decreaser can be used to reduce alkalinity and to lower pH. 

Can you lower alkalinity in hot tub naturally?

You can lower alkalinity using water but it is better for the hot tub if you use approved chemicals.

Should I raise pH or alkalinity first?

You should raise alkalinity first and then adjust to reach the right pH level. Good alkalinity levels will help prevent fluctuations in pH. 

Wrapping Up

If you’ve noticed the hot tub’s alkalinity levels are regularly too high then it may be an issue with your water source, pollutants in the water or chemicals. It’s important the total alkalinity level is reduced for your health and comfort as well as for the longevity of the hot tub. Reducing alkalinity is a straightforward job but remember that this will also change the pH level so test both the alkalinity and pH before using the hot tub again.

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