How To Raise pH In Your Hot Tub (When It Gets Too Low)



pH (Potential Hydrogen) measures how acidic or alkaline (basic) your water is on the pH scale.

The ideal pH level for your hut tub is equal to or between 7.4 and 7.6. Anything below this range will upset the balance of your water, and ultimately cause some undesirable side effects with your hot tub chemistry.

Let’s talk about what causes falling pH, why it’s important to keep an eye on it, and how to correctly raise the pH in your hot tub.

Why Your Tub Has Low pH

Water chemistry is a delicate balance at the best of times, and there’s various reasons as to why the pH level has taken a nosedive.

The most common reason a hot tub’s pH level falls is due to bather load. The amount of people the tub sees translates to more pollutants entering the water. 

People can bring anything from body oils, shampoo residue, sunblock, saliva, skin and hair fibers, and even urine into the tub. This uses up the sanitizer in the water, and if it’s not restored, the pH level will drop.

Outside pollutants are another reason. Things like rain water and backyard debris like leaves and dirt can all enter the tub and use up the sanitizer. Using a hot tub cover can alleviate this issue.

Other factors can be the water you’ve used to fill up the tub, or any chemicals you’ve added to the water. If the water source is acidic to begin with, your pH will test low, and acidic chemicals like chlorine and bromine can also drop the pH.

Why Low pH Is Bad News

A tub with a low pH level is bad news for bathers and for the tub itself. Here’s why you shouldn’t let the pH level stay low.

  • It causes chlorine inefficiency. Low pH water renders the sanitizer (usually chlorine) useless. It doesn’t matter how much you add, it just won’t work in low pH water. Ineffective sanitizer will allow a host of viruses, bacteria, and pathogens to take up space in your tub, and can make bathers extremely sick in the process.
  • It can damage your tub. The acidic nature of low pH water can eat away at your tub. Problems like etching of plaster surfaces, delamination and cracking of the shell can damage it beyond repair. It will also eat through any types of metals you may have on the tub, such as lights and railing fixtures.
  • It can damage your equipment. Low pH water will continue on from damaging your tub to damaging the equipment that runs your tub. As the water is constantly circulated, it will enter pipes, the pump, and the filter, causing destruction along the way. Repairing these can be costly and most of the time they have to be fully replaced.
  • It creates a breeding ground for algae. Couple the low amount of sanitizer in low pH water with a warm water temperature, and you’ll have a delightful algae bloom on your hands. Eradicating this green water problem can be a nightmare, as algae can get into the hot tub system as well. Draining the tub,  scrubbing it thoroughly, and flushing out the system is your only hope at that point.
  • It will irritate bathers. Low pH water is abrasive to humans. It will sting bathers’ eyes, give them itchy skin, and irritate their nasal passages and lungs. This abrasive water can also cause fading of swimsuit material.

How To Raise pH In A Hot Tub

Your tub should never have a low pH level for an extended period of time. Luckily there are chemicals you can add that will quickly restore the pH to a neutral level.

Method #1: Use Soda Ash (Sodium Carbonate)

Soda ash is the preferred method to raise the pH of your tub. This is because soda ash, with it’s own 11.4 pH level, has the most drastic effect on raising pH. 

Soda ash will also raise the total alkalinity (TA) level. But when it comes to raising pH in a hot tub, you can’t raise one without raising the other simultaneously.

Where TA is concerned, you need to keep it between 80 and 120 ppm. Its role is that of a buffer, protecting the pH from fluctuating all over the place. Without the proper TA level, the pH can erratically drop or peak, testing acidic one minute and alkaline the next.

Keeping the TA level stable makes all the difference, so after using soda ash you’ll have to check both levels to make sure the TA hasn’t spiked over 120.

Here’s how to add it to your hot tub:

  1. Start by testing the water (turn the jets off) using a testing kit. You can use test strips, a liquid test kit, or digital testing meter. These will all test for pH and TA levels. Take note of the pH level of the water.
  2. Measure out the amount of soda ash you want to add to the tub. There’s no set amount to raise the water by “X”, but a general rule is to use 1 tablespoon per 100 gallons of water. We’d recommend adding 75% of what you think you might need so you don’t overdose the tub.
  3. Soda ash is very safe to use and you can either pre-dissolve it by diluting it in a bucket of water, or pour the chemical directly into the hot tub. Diluting the ash will help disperse it better in the tub. If you choose to add the chemical on its own, ensure it’s mixed up well in the tub so undissolved granules don’t cling to the tub’s shell.
  4. Fire up the jets and circulate the soda ash for about an hour.
  5. Retest the water. Adjust the pH and TA levels if needed.

Method #2: Use Baking Soda (Sodium Bicarbonate)

Baking soda is the other method you can use to raise hot tub pH. 

It’s a popular method because it doesn’t raise the TA as much as soda ash will. However, the downside is that it’s not as effective at raising the pH. 

Baking soda’s pH level is 8.3, significantly lower than soda ash. This means you’ll have to use a lot more baking soda to raise the pH level, but the TA will be less affected.

Here’s how to add it to your hot tub:

  1. Turn off the tub jets and test the water using test strips, a liquid test kit, or a digital tester. Take note of the pH and TA levels.
  2. Adding baking soda isn’t an exact science. The rule is 1 tablespoon per 100 gallons of hot tub water. You’ll have to do a trial and error approach. Measure out the amount you think you’ll need for the tub.
  3. Add the baking soda to the tub. If you pour it directly into the water, mix it up well so that no granules stick to the shell floor or walls. You can also dilute the baking soda in a bucket of water, pre dissolving it for easier dispersion once it’s poured into the tub.
  4. Turn the jets back on and let the water circulate the baking soda for about an hour.
  5. Retest the water for both the pH and TA levels, and make any necessary adjustments.

How To Total Alkalinity Back Down

Now that you know using something like soda ash to raise the pH can also bring up TA in a big way, you may need to lower it when retesting.

TA can be lowered using either muriatic acid, or sodium bisulfate.

Muriatic acid is more commonly used due to its lower price. However, sodium bisulfate is a dry acid that is more safe for handling, as the former can cause major burns, and its fumes can induce respiratory distress if you’re not careful.

Either one will work fine, it just depends on your budget and how comfortable you are working with acid.

Pick Your Poison!

You can’t go wrong with soda ash or baking soda if you need to raise the pH in your hot tub.

By using these chemicals, you’ll be able to keep the water properly balanced, leading to clean water around the clock, less overall chemical usage, and more time in the tub for you and your family.

Categories: Hot Tub Care, Hot Tub Chemistry