How To Lower Alkalinity In Your Hot Tub (2 Easy Methods)



Total alkalinity (TA) keeps the pH level in your hot tub stable by neutralizing acids in the water. It’s basically a pH buffer.

Like swimming pools, the ideal range for alkalinity in your spa or hot tub is between 80 and 120 parts per million (ppm). Anything outside that range will ultimately lead to issues with your water chemistry.

Let’s talk about why alkalinity rises, why it’s important to keep an eye on it, and how to correctly lower alkalinity in your hot tub.

Why Your Tub Has High Alkalinity

The level of total alkalinity in the water is tied directly to the water’s pH level. If the pH level rises over 7.6, it becomes alkaline or basic. This will gradually increase the TA of the hot tub water as well.

Rising pH and alkalinity is due to a few factors, with the first being pollutants in the water. This can be anything from backyard leaves and debris, to body oils, sunblock, and anything else that may be on a bather’s body prior to entering the tub.

High alkalinity can also be the result of shocking, a process that kills off everything in the water via a mass dose of chlorine. TA can spike after this because chlorine-based shock is highly alkaline.

Finally, simply refilling the tub after a drain can cause a TA increase. This isn’t always going to happen but if the water source you’re using leans to the alkaline side of the scale, you’ll end up with high TA in the tub.

Why High Alkalinity Is Bad News

Everything in moderation, right? That rule is no different when it comes to water alkalinity. Here’s what happens if the TA level gets too high in your tub:

  • Scale will build up. You’ll start to notice scale floating on the surface of the water. This is due to the increase in calcium that comes with high alkalinity. Not only is it a nuisance to deal with, but it can also damage your hot tub equipment with deposit build up if it gets into the system.
  • Cloudy water happens. Another side effect of having too much calcium in the hot tub is the water turning cloudy. This is more cosmetic, but is a good indicator of high TA in the tub.
  • Chlorine won’t work as well. As the TA increases, so does the pH, and this causes the chlorine to become less effective over time.
  • Irritation issues. An unbalanced pool can lead to the irritation of swimmers’ eyes, skin, and even nasal passages. Additionally, it can cause fading of swimsuit fabrics and can slowly eat through plastic goggles.
  • The pH level rises. High alkalinity means high pH. Not only will you have to lower the TA level, but also the pH. This can be a time consuming process if you have to do multiple rounds of water testing to get the proper balance of levels in the water.

How To Lower Total Alkalinity In A Hot Tub

When some chemical levels get too high, there is no fix for them. This is not so for alkalinity, and you can use acid to bring it down to an ideal level.

Safety note: When using these methods and diluting acid with water, always wear protective eyewear, chemically resistant gloves, and only ever add acid to the water – never the other way around!

Method #1: Use Sodium Bisulfate

Sodium bisulfate is a dry acid that is safe to work with, and easy to add to your hot tub. With dry acid, you need to ensure that moisture doesn’t get inside its container, so storing it properly is a must.

Here’s how to add it to your hot tub:

  1. Start by testing the hot tub water. You can use either test strips, a liquid kit, or a digital tester to get the total alkalinity level of the water.
  2. Consult the directions on the bottle to properly measure out how much sodium bisulfate you’ll need. In general, 3.5 ounces of acid will lower a 1,000 gallon tub by 10 ppm. Depending on the size of your tub and your current alkalinity level, you may need more or less.
  3. Using a 5 litre plastic bucket, scoop out water from the tub so the bucket is three-quarters full.
  4. Add the measured amount of sodium bisulfate to the water.
  5. Using a wooden stir stick, mix up the solution of acid and water until all the sodium bisulfate granules are dissolved. Undissolved acid granules may damage your hot tub shell if you’re not careful!
  6. Once dissolved, pour the solution into the hot tub.
  7. Give it some time for the water to circulate the chemical throughout the tub.
  8. Retest for total alkalinity and adjust if needed.

Method #2: Use Muriatic Acid

Muriatic acid is the other way you can reduce the alkalinity level in your hot tub.

Also known as hydrochloric acid, handling this chemical should be done with the utmost of care as it can burn skin, and the fumes can burn nose and lung lining, and it can even cause permanent eye damage.

Regardless, this is the more common way to reduce alkalinity in the hot tub, as it can also kill mold and remove calcium deposits.

  1. To lower the alkalinity by the widest margin possible, start by turning off the hot tub pump. Muriatic acid works best in still water. 
  2. Test the water with your testing kit to get the current TA level.
  3. Consult the directions on the bottle to properly measure the amount of muriatic acid you’ll need to add to the tub. 
  4. To make the acid more safe to handle, dilute the measured amount by adding 1 part acid to 10 parts water. Use a large plastic bucket and mix the solution using a wooden stir stick.
  5. Carefully add the solution to the hot tub. Make sure it doesn’t splash on exposed parts of the shell so it doesn’t get damaged.
  6. Wait about an hour for the solution to dissipate in the tub.
  7. Turn the pump back on and retest the water. Adjust the appropriate levels if needed.

How To Bring Your pH Back Up

After you’ve dropped your TA level, you may notice the pH level is now lower as well. There are a few ways you can bring the pH back to a neutral level.

You have 3 options: soda ash, baking soda, or aeration.

Soda ash and baking soda are usually the go-to methods, but they have an unwanted side effect of also raising the TA (especially soda ash). If you don’t want to be balancing your water for hours, you might want to try aeration.

By aerating the water, oxygen is infused into it. This removes carbonic acid and raises the pH level at the same time.

There are aeration devices you can buy that attach to your tub’s return jets to help introduce oxygen into the water. However, due to a hot tub’s design, the jets are already bubbling water at the surface. You can aerate the water by simply running the jets for an extended period of time.

Pick Your Poison!

At first, balancing various chemicals can be tricky when learning to lower alkalinity in a hot tub.

But by using sodium bisulfate or muriatic acid, you can keep the tub’s TA at a healthy level so the pH stays balanced and you can enjoy a relaxing soak.

Categories: Hot Tub Care, Hot Tub Chemistry