How to Balance the pH in a Hot Tub

How to balance the pH in your hot tub harbor hot tubs

by Swim University

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.

Before the cloudiness and scale caused by high or low pH in your hot tub starts causing you more serious problems, get your water chemistry under control.

What’s Important About pH in Your Hot Tub?

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 measure pH with test strips or a meter, it shows how acidic or basic your hot tub water is. Ideally, pH levels in your spa should measure between 7.2 and 7.6 parts per million (ppm)—as close to that neutral seven as possible.

If your spa’s pH measures outside that neutral range, you could be in for some unhealthy and potentially damaging water symptoms in your spa, such as bacteria growth or corrosion.

Low pH in Your Hot Tub

Any pH level below 7.2 ppm 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. Acidic hot tub water may also corrode spa components, which can be expensive to replace once the damage has been done.

High pH in Your Hot Tub

When your pH levels climb beyond 7.6 ppm, 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 hot tub water is another symptom of high pH in your hot tub.

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 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 125ppm–150 ppm.

When you adjust your alkalinity, add small doses, one at a time. Allow the 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.

Fix pH Levels in Your Hot Tub

When you have acidic water (low pH), you’ll add basic 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.

Raise pH only

If you want to increase your pH without touching your TA, you’re in luck. Only one product exists that can do this—magnesium oxide. While it may raise your TA, the increase is minimal compared to other pH up options. It’s a little unusual to find yourself with low pH and perfect TA, but if you do stick with those pH increase products that list active ingredient as magnesium oxide.

Raise pH and TA

The most common pH increaser products available to treat low pH in hot tubs contain the active ingredient sodium bicarbonate. You might recognize this chemical by its household name—baking soda. It really is the same stuff you keep in your fridge to eliminate odors.

Sodium bicarbonate is so good at increasing both pH and TA, you’ll notice it is the active ingredient in both alkalinity increasers and pH increasers.

Sodium bicarbonate has a stronger effect on TA than pH. This is useful to know in case you’ve recently lowered your pH and your TA fell with it. Use small doses of alkalinity increaser to bring your TA back up without raising pH too much.

Lower pH

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 won’t become an endless pH rollercoaster ride.

Muriatic acid is an alternative way to decrease both pH and TA. Because it’s an extremely caustic chemical, you must use protective glasses and chemical-resistant gloves and a whole lotta caution when working with it.

You won’t be able to just pour some in your spa, either. You’ll need to dilute it, add it to your spa, then aerate it by running your jets. Finally, you’ll leave your spa to circulate overnight before retesting your 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 your jets to clean out 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 source water.

Use a Hose Filter

This is an in-line carbon or charcoal filter that can easily be attached to your hose, and make your fill water so clean you could drink it. Hose filters are 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.

Use Metal Sequestrant

This additive attaches to metal contaminants in your spa water and keeps them suspended so they can’t settle on surfaces and cause staining. While using metal sequestrant won’t directly affect your pH, it will help prevent buildup and staining that can occur when low pH allows metals to come out of your solution to cause problems.

Use a maintenance dose of metal sequestrant every week (or as often as your product recommends) prior to balancing your water.

Remember to always test your chemistry before adding any chemicals, then test again after each adjustment. Always give additives enough time to circulate before testing or adding anything else.

Back To The Basics

Keeping your lines, filter, and water clean will prevent a whole host of water chemistry problems. Always change your water completely every three or four months so you’re not fighting to balance dirty water. Remember, having a higher bather load (more use) and chemical imbalances might require you to drain and refill your hot tub even more often than that.

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

Happy Soaking!

If you have additional questions or would like to schedule your spa's maintenance please click here

Ian Fyffe