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How to Balance Hot Tub pH

By Matt Giovanisci | Updated: March 4, 2021

You got a hot tub so you could kick back, relax, and unwind. But instead, unstable pH levels and screwed-up total alkalinity (TA) levels are driving you mad. You’re chasing chemical levels up and down your test strips, but you just can’t seem to hit the sweet spot in the middle.

First, the pH is too low, so you figure out how to raise the pH in your hot tub. But it goes too high, so you have to get a handle on how to lower the pH in your hot tub. You’re starting to feel like Goldilocks in a nightmarish fairytale where there’s no just right. Only all wrong.

Never fear. You can get your water chemistry under control before the big bad wolf—actually, cloudiness and scale deposits—huffs and puffs and blows your hot tub down. Or something.

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What’s Important About Hot Tub pH?

You might remember acids and bases from high school chemistry. When a solution (that’s a chemical mixed with water) contains extra hydrogen ions, it’s acidic. When the solution has fewer hydrogen ions than plain water, it’s basic.

On the general pH scale, seven is perfectly neutral water. Lower numbers are more acidic, and higher numbers are more basic.

When you test your hot tub water with test strips or a liquid test kit, they’ll show how acidic or basic your hot tub water is. Ideally, pH levels in your spa should measure between 7.4 and 7.6.

If your spa’s pH measures outside that range, you could be in for some unhealthy and potentially damaging water symptoms in your spa.

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Low pH in Your Hot Tub

Any pH level below 7.4 could spell trouble. The lower the pH level, the more acidic your hot tub water is. Highly acidic water makes it more difficult for your sanitizer to work effectively, leaving bathers in your hot tub exposed to potentially harmful contaminants.

This increases your chances of being exposed to bacteria, such as pseudomonas aeruginosa (the cause of hot tub folliculitis) or legionella (which causes Legionnaires’ Disease), among others. Low pH in your hot tub may also cause corrosion in spa components, which can be expensive to replace.

High pH in Your Hot Tub

When your pH levels climb beyond 7.6, your spa water can be described as basic. What this means for you is poorly sanitized water, carrying the same risks as any other cause of ineffective sanitizing.

Basic spa water is also prone to forming scale and drinking pumpkin spice lattes year-round. Kidding—it’s not that kind of basic. But it really will cause flaky scale to build up on your spa surfaces.

The scale is due in part to high calcium hardness caused by the high pH. Cloudy water is another symptom of a high pH level in your spa.

What Does Total Alkalinity Mean?

You came here to learn how to balance the pH in your hot tub, so what’s this about total alkalinity? Well, the term technically refers to the ability of a solution to neutralize acids—or buffer them.

In your hot tub, the importance of measuring total alkalinity (TA) is only slightly different. TA acts as a buffer for the pH level in your water, keeping the pH level stable while allowing you to adjust TA without throwing the rest of your hot tub chemistry into chaos.

Total alkalinity is so important to your water balance, the first step in your water care process will always be measuring and adjusting TA before any other chemicals. The ideal range for TA is 100 parts per million (ppm) to 150 ppm.

To adjust alkalinity, add alkalinity increaser in small doses, one at a time. Allow each dose to circulate before testing again. Only after your TA is in the optimal range should you move on to adjusting pH. Achieving the right TA may actually get your pH in the target range.

Balancing Your Hot Tub’s pH

When you have acidic water (low pH), you’ll add alkaline chemicals to increase the pH. When you have basic water (high pH), you’ll add acids to lower the pH. So you’ll get your TA perfect and then add some other stuff to fix your pH, right? Not exactly.

Using certain types of pH increaser or pH decreaser will likely also affect TA. This is why getting these two levels balanced can be tricky, but not impossible.

How to Raise the pH in Your Hot Tub

Most pH increasers contain the active ingredient sodium carbonate. You might recognize this chemical by its more common name—soda ash.

You may be thinking, that sounds an awful lot like sodium bicarbonate—baking soda. You’re right. They’re closely related, and baking soda will also raise the pH in your hot tub. But it’s not nearly as effective as soda ash. So when you’re considering how to raise the pH in your hot tub, choose soda ash over baking soda, and you’ll save yourself a lot of time and trouble.

Sodium bicarbonate is actually much better for raising TA, especially if you don’t want to affect the pH level too much.

It’s important to note that soda ash can also dramatically increase total alkalinity. So if your hot tub pH is low, but the total alkalinity is normal or high, sodium carbonate may increase the alkalinity beyond the recommended maximum level.

Also note that soda ash can make your hot tub water cloudy, so if you use it to lower pH levels, you may have to address a cloudy hot tub afterward.

How to Lower the pH in Your Hot Tub

Typically, the active ingredient in pH decreaser, sodium bisulfate, will also lower TA, sometimes so significantly you’ll need to bump your TA back up a little afterward.

Sodium bisulfate also helps stabilize pH, so if you do need to tweak your TA, it’s less likely to become an endless pH rollercoaster ride.

Muriatic acid is an alternative way to decrease both pH and alkalinity. Because it’s an extremely caustic chemical, you must use safety glasses, chemical-resistant gloves and a whole lotta caution when working with it. Here’s more information on lowering hot tub alkalinity.

To be even safer, you can use a muriatic acid replacement product that’s not as caustic. You’ll still need to wear the safety gear, though.

It’s not the best idea to just pour muriatic acid directly into your spa. You’ll need to dilute it, add it to your spa, then aerate it by running the jets. Finally, leave your spa to circulate overnight before retesting the water.

Start pHresh

The truth is, you shouldn’t have to chase around low and high pH in your hot tub. If you find yourself doing so, the easiest option is probably to drain your spa and start over.

The day before you drain, add some line flush, and run the hot tub to clean out the plumbing and remove anything that could be affecting your water chemistry. After draining, clean the interior of your spa.

If you’re like most hot tub owners, you use your hose and outdoor spigot to fill your hot tub. Even if your water is from a municipal source, it could still have high chlorine content or contain problematic amounts of metal causing hard water.

Both issues can complicate your quest for balanced water chemistry. You can take two simple precautions to limit problems caused from a poor water source.

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Use a Hose Filter

What’s the best way to keep metals and other contaminants out of your hot tub? Don’t let them in there in the first place. By using a hose filter when you fill or add water to your hot tub, you end up with, not perfect, but much cleaner water than if you just filled it directly from the spigot.

A hose filter can easily be attached to your hose, and it’ll make your fill water so clean you could drink it. Not that you’d want to. Hose filters are usually used for RV water lines to make sure potable water sources are truly clean enough to drink from the RV tap. Most versions have hose connectors, so you can screw them in place by hand without any tools at all.

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Use Metal Sequestrant

Even with a hose filter, some stuff is going to get through. No filter is absolutely 100% effective. If your water source has high levels of dissolved metals like iron and copper, add a dose of metal sequestrant whenever you refill or add any fresh water to your hot tub.

Metal sequestrant doesn’t take metals out of your water. Instead, it bonds with them and keeps them suspended in the water so the filter can more easily grab them. It also keeps them from settling on your hot tub’s surfaces and staining them.

While using sequestrant won’t directly affect your pH, it will help prevent buildup and staining that can occur when the water’s pH level is too low.

Remember to always test the water before adding any chemicals, then test again after each adjustment. You’ll need to use special test strips made to measure metals. Then give additives enough time to circulate before testing or adding anything else.

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01/25/2023 02:41 pm GMT

Back To The Basics

Keeping your lines, filter, and water clean will prevent most chemistry problems, as well as the effects poor water chemistry can have on your hot tub and your health. Remember to change the water completely at least every three or four months so you’re not fighting to balance dirty water.

Stick to a hot tub water care plan that works for you and your spa, and you’ll head off most water problems before they even begin.

Happy Soaking!

Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1995. Since then, his mission is to make pool and hot tub care easy for everyone. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
A Cheat Sheet For Balanced Hot Tub Water and Crystal Clear Soaking.
Download this FREE printable cheat sheet to keep your hot tub clean and clear. You’ll never worry about your hot tub again with this easy-to-use guide.
Click Here For The FREE Cheat Sheet