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Everything You Need to Know About Hot Tub Alkalinity

Updated: Nov 11, 2023

Hot tub owners can have a lot of fun, but there are also specific responsibilities if you want to enjoy a safe and relaxing hot tub experience.

Keeping your hot tub clean is the priority, along with the all-important water chemistry. A critical part of hot tub care is ensuring the hot tub's alkalinity level and pH balance are okay.

If you want to know more about alkalinity balancing, keep reading.

  • Discover why the correct level is so important

  • Learn what that level should be

  • How to test total alkalinity

  • Why alkalinity drops

  • The best methods for lowering or raising alkalinity levels

What is total alkalinity in a hot tub?

Total alkalinity is a term that refers to how well the water in your hot tub can neutralize acids or how buffered it is.

The total alkalinity level (TA level) is not a relative measure. It measures the concentration of carbonates, hydrozises, bicarbonates, and other alkaloids in hot tub water. The hot tub's alkalinity is measured in parts per million or ppm.

What should water alkalinity levels be?

Ideally, the alkalinity in your hot tub water should have a total alkalinity level of 80 to 120 ppm. It is vital to maintain the right level for best results.

How are pH and alkalinity related?

The pH and alkalinity of your hot tub water are connected but also very different. It's a common misconception that the water's pH and alkalinity are the same, but this couldn’t be further from the truth.

Hot tub water is described as being ‘basic’ when it is more than seven on the pH scale. However, the same does not apply to alkalinity. Water alkalinity specifically relates to the amount of acid the hot tub water can neutralise.

When you dissolve an alkali in your hot tub’s water, it improves its ability to neutralise any acid. Total alkalinity, or TA for short, is a measurement of the amount of alkali dissolved in the water. The proper level should be between 80 and 120 parts per million.

When the water in your hot tub is at the correct total alkalinity level, it will be able to deal with any changes in the pH level much better and resist any unwanted effects. That is the relationship between alkalinity and pH.

How to test total alkalinity in a hot tub?

The first and most crucial step is to test the alkalinity in your hot tub water. It plays a vital role in any hot tub maintenance schedule.

It’s straightforward to do using spa water test strips and testing kits that you can purchase from many spa stores, hardware stores, and online.

Whichever method you use, you must follow the instructions of the hot tub manufacturer. Even if the total alkalinity level is perfect, test the hot tub water regularly. Twice weekly should be more than adequate. Total alkalinity levels can change very quickly.

Why is my hot tub alkalinity high?

When you test your hot tub water for total alkalinity, it’s not going to be high very often. However, several things can cause a high alkalinity level.

Let’s look at some common causes of high hot tub alkalinity:

  • Too many chemicals: If you add more chemicals than you need to, it will increase the TDS or Total Dissolved Solids. You must drain, clean, and refill your hot tub once every quarter to stop this from happening.

  • Too much sweat, perfumes, lotions, and similar can raise the alkalinity level: It could be you, your family, or friends who are raising the levels. You should always take a shower before you take a soak in your hot tub. This will remove any lotions, gels, perfumes, sunblocks, sweat, and similar things.

  • The source of your water: you might live where the water has naturally high alkaline levels. Don’t be afraid to ask your water provider to take a reading to check the levels.

  • You’ve made a mistake: It could be something as simple as using too much baking soda or other alkalinity increaser product.

Is high alkalinity in a hot tub bad?

If the total alkalinity of your hot tub water is too high, several things could happen, all of which are bad.

Firstly, increasing alkalinity affects the sanitiser and could make it useless. This applies whether you use bromine or chlorine. If the sanitiser isn’t being effective, the water in your hot tub could turn a nasty shade of green. It might also become a breeding ground for bacteria, making your hot tub very unsafe.

The second issue relates to scale. You could have to deal with a build-up of scale. This means your hot tub will have to work overtime to keep the water at an optimum temperature. It also puts you at risk of skin issues such as spa folliculitis or itchy dry skin.

Finally, a high level of alkalinity could be very stressful for your wallet. You may need to spend money on repairs before you plan to add extra sanitising chemicals.

Is it safe to swim if alkalinity is high?

Because of the issues mentioned previously, the answer has to be no. It's not safe to swim if alkalinity is high. Even if you have pH balanced water, you need to lower alkalinity levels using a pH decreaser.

Does high alkalinity cause cloudy water?

Yes, there are occasions when high alkalinity can lead to cloudy water. The reason for this is that there is an imbalance in the pH level, which can lead to calcium scaling and, ultimately, cloudy hot tub water.

How do you reduce alkalinity in a hot tub without lowering pH?

It’s possible to lower alkalinity very quickly if you find the level is more than 120 ppm. Adding sodium bisulfate or muriatic acid is a very effective way. Here are the steps to follow:

  1. Work out the amount of sodium bisulfate needed. It depends on the volume of water in the hot tub and how much you need to lower the TA. As a guide, 3.5 ounces of sodium bisulfate will lower the TA of 1,000 gallons by around ten ppm. If your hot tub only contains 500 gallons, you’ll only need to add 1.75 ounces to lower the alkalinity by ten ppm.

  2. Measure out the right amount of sodium bisulfate.

  3. Turn on the hot tub circulation and add the correct amount of sodium bisulfate.

  4. Let the water circulate for around twenty minutes before switching it off.

  5. As soon as the water is still, wait an hour before repeating the total alkalinity test.

  6. If the level is still too high, repeat the previous steps.

  7. You can stop once the total alkalinity is at the correct level.

  8. Leave your hot tub overnight and then test it again just to make sure the level is still correct.

What causes low alkalinity in a hot tub?

Humans are most often the cause of low total alkalinity in a hot tub, especially if you use your hot tub frequently. Unfortunately, you can bring in a lot of pollutants when you soak in your hot tub, which alters the chemistry of the water. The pollutants range from sweat and possibly even urine to a chemical residue that might be in your swimsuit and body oils.

Mother Nature might also have something to do with a low alkalinity level. Rainwater is often more acidic than alkali, which means it could lower the alkalinity of your hot tub’s water. However, this wouldn’t be such an issue if you used a cover for your hot tub.

Finally, if you use chlorine tablets, they could also be causing a low alkalinity level. This is because chlorine tablets lower a hot tub’s pH level.

Can you go in a hot tub with low alkalinity?

It is not advisable to use hot tubs with low levels of total alkalinity. A hot tub with low alkalinity can have the following problems:

  • Green water: Algae blooms can be a serious issue when alkalinity levels drop.

  • Corrosion issues: Even if your hot tub is fibreglass, corrosion can still be an issue. However, it’s even more serious if your hot tub has a metal surface. It can also be detrimental to the internal workings of the pump and its filter. Corrosion issues could mean your pump and its filter will need to be replaced, which would be very costly.

  • Fluctuating pH levels: When there is insufficient alkalinity in your hot tub water, it means the pH level will fluctuate wildly. This is known as the pH bounce. It happens because the water has an insufficient pH buffer.

  • Skin irritation: The hot tub water becomes very acidic when the alkali levels are low. Anyone soaking in the tub will find this very irritating for their skin, nasal passages, and eyes. It could even lead to respiratory distress.

  • Tub damage: The damage that could occur depends on the material of your hot tub. But it might include cracking, etching, staining, and delamination. If you use a vinyl cover, this could also become brittle and stiff.

How do you increase total alkalinity levels?

Low alkalinity levels in hot tubs are a serious problem. But there are a few options to increase the levels. Here's how to increase alkalinity in hot tub water.

Baking Soda Method

Sodium bicarbonate or baking soda is commonly used to raise total alkalinity levels in hot tubs. You can buy various alkalinity increaser products, for example, Alkalinity Up or Alkalinity Increaser. Most branded alkalinity increasers are just baking soda marketed in an attractive bottle.

The benefit of baking soda is that it’s a very safe chemical to use. You can handle it without problems, pour it into your hot tub directly, and buy it from your local grocery store. The generic product will also be cheaper than a specially packaged alkalinity increaser.

You’ll also be pleased to learn that it will raise the alkalinity level but have minimal impact on the pH scale.

Here are some steps to follow:

  1. Test your hot tub water using a digital tester, test strip, or a testing kit.

  2. Calculate the amount of baking soda needed to raise the total alkalinity level so that it’s a minimum of 80 parts per million.

  3. Measure out the correct amount according to your calculations. Generally, you’ll need one tablespoon of sodium bicarbonate if your hot tub contains 100 gallons of water.

  4. Wear goggles and rubber gloves to protect yourself.

  5. Dilute the baking soda with water in a bucket. Make sure it’s completely dissolved.

  6. Pour it into the hot tub and circulate the water for around 20 minutes.

  7. Use another test strip to retest the water and, if necessary, repeat the retesting process.

Soda Ash Method

You can also use soda ash, otherwise known as sodium carbonate, to counter the low total alkalinity level in hot tubs.

The main difference with this method is that it will also act as a pH increaser and raise the pH level. This could be an issue if there’s nothing wrong with the pH reading at the time.

Here are some steps to follow:

  1. Test the hot tub water sample using test strips, a digital tester, or a testing kit.

  2. Use the same amount of soda ash as you would baking soda. In other words, one tablespoon for one hundred gallons of water.

  3. Protect yourself by wearing protective eyewear and rubber gloves.

  4. Add the required amount of soda ash to a bucket of water.

  5. Use a wooden stick to stir the solution until the ash has dissolved completely.

  6. Pour the mixture directly into the home spa.

  7. Allow the tub to circulate the water for a few hours.

  8. Use a fresh test kit to retest the water and repeat the process if necessary.

How do I raise alkalinity without raising pH levels in a hot tub?

Whatever you do to raise alkalinity quite often affects the pH as well. However, pool owners commonly use aeration to deal with both pH and alkalinity imbalance. It will lower total alkalinity but not raise pH levels.

You circulate air into the water every time you need to raise the total alkalinity level in your home spa. Allowing some form of movement also helps. For example, you could hire an air pump and insert the hose into your hot tub to add air flow to the water.

Best hot tub chemicals to balance your hot tub

To keep your water clean and fresh, we recommend testing your water at least twice a week. But knowing which are the best hot tub chemicals to suit your needs can be difficult. At Aqua Spa Supplies and Aqua Warehouse, we specialise in providing a range of high quality hot tubs for sale and hot tub accessories to ensure your spa is kept safe, fresh and clean.

If you would like more information about our vast selection of hot tub chemicals,visit our websiteor call us today on 01245 477 400.


Keeping a close check on total alkalinity levels plays a crucial role in hot tub ownership and hot tub water care. You should be monitoring your hot tub water and testing it regularly, at least two times every week. Doing so will identify any imbalance in the chemical levels, low pH or high pH levels and allow you to take any necessary steps.

Not only will this increase the life of your hot tub, but it will also ensure your hot tub experience is a safe, healthy, and pleasurable one.


1. Does pH UP increase alkalinity?

When you add pH increaser product to increase low pH water to a high pH level, it can also raise alkalinity.

2. What should be adjusted first, alkalinity or pH?

This depends on the situation. For example, if both alkalinity and pH levels are low, it’s best to raise alkalinity first. You can then test the water again. If the hot tubs pH level is still on the low side and total alkalinity is within the ideal range, add some soda ash or baking soda.

3. Will alkalinity lower on its own?

The only way that the total alkalinity can reduce on its own is if rainwater is allowed to enter your hot tub.




Jess Court

I'm Aqua Warehouse Groups Marketing Officer - overseeing all things news worthy in the hot tub industry, with tips and tricks that are bound to make a splash.

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