Hot Tub Chemistry Guide: How Do I Raise or Lower Alkalinity and pH?

Ever stare at your hot tub test strip wonder why your water chemistry refuses to cooperate? Spa pH and alkalinity continue to confuse owners. Furthermore, Shasta Pool Supply fields calls every week from frustrated hot tub owners. These spa owners feel they're playing a losing game of chemical roulette.

Here's what you need to know: pH should sit between 7.2 and 7.8. Additionally, total alkalinity belongs in the 80 to 120 parts per million (ppm) range. Sounds simple enough, right? However, levels test fine one day and swing overnight. Therefore, the out of chemical balance causes cloudy water, weak sanitizer, or white chalky buildup.

Getting your alkalinity and pH levels right doesn't require a chemistry degree. Specifically, total alkalinity works as your pH's bodyguard. Therefore, it buffers against those annoying sudden changes. That's why smart hot tub owners always tackle alkalinity first before messing with pH. Once you understand how these two work together, you'll spend way less time fussing with chemicals. Now, stop guessing and start getting results. Let's break down exactly how to get your hot tub water balanced and keep it that way.

You've probably heard these terms thrown around, but here's what they actually mean for your hot tub—and why getting them right matters more than you might think.

What is pH and why it matters

pH measures how acidic or basic your hot tub water is on a scale from 0 to 14. Think of 7 as neutral—like pure water. Numbers below 7 mean acidic, numbers above 7 mean basic (alkaline).

This isn't just chemistry class trivia. When pH goes wonky, your hot tub fights back. When pH is too low, the water becomes acidic. This eats away at your heater, pump, and metal parts, and it can also make your eyes and skin sting. High pH creates its own headaches—chalky buildup, cloudy water, and here's the kicker: at pH 8.2, your chlorine becomes only 15% effective. So much for that "sanitized" soak.

What Are the Best pH and alkalinity Levels for a Hot Tub?

Your pH sweet spot sits between 7.2 and 7.8. Most pros push for the tighter range of 7.2 to 7.4 because it gives you the best performance. For total alkalinity, aim for 80 to 120 ppm. Some experts recommend staying closer to 120 ppm to minimize those pH swings.

Here's the thing: these two work as a team. Stabilized alkalinity typically settles your pH right around 7.5—exactly where you want it. That's why the golden rule exists: fix alkalinity first, then worry about pH. Skip this order, and you'll be chasing your tail with chemical adjustments that never seem to stick.

Why Do My Hot Tub’s pH and Alkalinity Get Out of Balance?

Hot tub chemistry problems don't just happen randomly. After decades at Shasta Pool Supply, we've seen the same culprits mess up water balance over and over again. Here's what's really going on behind the scenes.

Body oils, lotions, and detergents Mess Up Hot Tub Water

Here's something most people don't realize: every time you get in your hot tub, you're basically adding a cocktail of contaminants to the water. Even if you shower beforehand, your body still releases oils, sweat, and traces of whatever products you've used that day.

The numbers are pretty shocking. Just four people in a small hot tub make the water as dirty as 250 people in a big pool. That’s how fast oils and sweat build up. Think about that for a second.

Lotions, makeup, sunscreen, and hair products don't just disappear in hot water—they wash off and create perfect conditions for bacteria to thrive. Those detergents from your swimsuit? They're causing foam and throwing off your pH balance. Hot water makes it worse because it pulls natural body oils out of your skin faster than you'd expect. 

Mother Nature isn't doing your hot tub any favors. Leaves, pollen, dust, and general outdoor debris constantly find their way into your water, messing with clarity and chemistry.

Rainwater might look clean, but it dilutes your carefully balanced chemicals and can actually encourage algae growth by weakening your sanitizer levels. We get calls about this all the time after Arizona's monsoon season.

Overuse of spa chemicals

This one's going to sound backward, but bear with us. Sometimes the chemicals meant to fix your water problems actually create new ones. We see customers dump in shock treatments or pH adjusters, thinking more is better, only to end up with bigger headaches.

Shock that doesn't dissolve completely makes your water cloudy. Those copper-based algaecides? Mix them with high chlorine and you'll get that lovely green tint nobody wants.

Water source and mineral content

Your tap water isn't neutral—it comes with its own chemical baggage. Hard water loaded with calcium, magnesium, and other minerals can push your pH levels up before you even add chemicals. Iron-heavy water causes staining that's a real pain to deal with.

If you're constantly fighting high alkalinity, your water source might be the real problem. High alkalinity in your fill water makes chlorine and bromine work poorly. That's why we often tell customers to invest in a pre-filter when filling their hot tubs—it saves headaches down the road.

pH and Alkalinity Levels

Here's where the rubber meets the road. You know what levels you're aiming for, you understand why your water gets out of whack—now let's fix it. At Shasta Pool Supply, we've walked thousands of hot tub owners through these exact steps since 1966.

The key? Always tackle alkalinity first, then pH. Trust us on this one.

How Do I Test Hot Tub Water the Right Way?

Testing your water isn't rocket science but doing it right matters. Grab your test strips or liquid test kit and check your levels 2-3 times weekly. Here's how to get accurate readings every time:

1. Collect water from elbow-deep in your hot tub, away from jets
2. Dip the strip briefly—no need for extended soaking
3. Hold the strip still for approximately 15 seconds
4. Compare colors to the provided chart

Skip the guesswork. If your colors don't match the chart exactly, take your best guess between two shades.

How to raise alkalinity in a hot tub

Low alkalinity means your pH will bounce around like a ping-pong ball. Fix alkalinity before you even think about pH.

Reach for sodium bicarbonate (baking soda) or a dedicated alkalinity increaser. For a 400-gallon hot tub, add 1.25 ounces of baking soda to bump alkalinity up by 10 ppm. Run your jets for circulation, then retest to confirm you've hit that 80-120 ppm sweet spot.

How to lower hot tub alkalinity

When alkalinity runs too high, pH decreaser (sodium bisulfate) becomes your best friend. Sprinkle it evenly across the water surface while your jets are running—don't just dump it in one spot.

Start with 3 ounces of pH decreaser per 1,000 gallons to drop alkalinity by about 10 ppm. Wait 24 hours before retesting and making another adjustment if needed. Patience pays off here.

How to increase pH in hot tub

If alkalinity looks good but pH is still too low, add a pH increaser (sodium carbonate). This gently brings your water back to balance.
Want a natural alternative? Borax works great—about 4 teaspoons per 500 gallons will raise pH by 0.5-1.0 without messing with your alkalinity much. Run those jets for at least 30 minutes before you retest.

How to adjust pH in hot tub after alkalinity change

Here's what many hot tub owners don't expect: fixing alkalinity will often shift your pH too. That's normal.

Let your jets run for 20 minutes after adding any chemicals. Then retest both parameters before you make any more adjustments. Remember what we said earlier about alkalinity being pH's bodyguard? Once alkalinity is stable, pH becomes way easier to manage.

How Do I Keep My Hot TubTips to Maintain Balanced Water Chemistry Balanced?

Here's what we've learned after decades of helping hot tub owners: fixing problems costs way more time and money than preventing them. At Shasta Pool Supply, we've watched too many customers struggle with the same avoidable issues.

Skip the headaches. These five practices will keep your water crystal clear without the constant chemical adjustments.

Test water 2-3 times per week

Testing isn't optional—it's your early warning system. For chlorine or bromine systems, check your levels every two days. pH needs daily attention to stay between 7.4 and 7.6. Calcium can wait—test it every two weeks.
Always test with jets running and grab your sample from at least 12 inches deep. Surface water lies to you.

Use a pre-filter when filling your spa

Your tap water brings baggage. Sediment, metals, and who-knows-what-else from municipal systems will throw off your chemistry before you even add the first chemical.

A decent pre-filter handles 10,000-30,000 gallons and pays for itself by reducing your chemical needs. Think of it as insurance for your water quality.

Rinse off before entering the hot tub

Body oils, deodorant, makeup, cologne—everything you wear gets dumped into your spa water. Even a quick rinse removes sweat, dead skin, and product residue that would otherwise overwork your filtration system.

This one step alone dramatically reduces chemical demand and keeps your water cleaner longer.

Drain and refill every 3-4 months

Fresh starts work. Complete water changes every 3-4 months flush out dissolved solids that no filter can catch. Heavy users need to drain every 2-3 months, light users can stretch to 4 months.

Watch for the warning signs: cloudy water that won't clear, persistent foam, or chemicals that just won't stick. When your water fights back, it's time to start over.
Avoid overtreating with chemicals

More isn't better—it's dangerous. Overdosing chemicals damages your spa's interior, irritates skin, and can cause breathing problems. Always wear gloves and goggles when handling spa chemicals.

Read every label. Twice. Following dosage instructions keeps you and your equipment safe. 

Hot tub chemistry doesn't have to be your nemesis. Once you understand that alkalinity comes first and pH follows, you've cracked the code that trips up most spa owners.

Here's what you now know that most people don't: Your water chemistry problems usually have simple causes. Body oils, environmental debris, and yes, even your own good intentions with chemicals can throw things off. But you're equipped to handle it.

Test regularly. Adjust alkalinity first. Let pH settle into place. Shower before soaking. Use a pre-filter.

Simple steps, but they work.

At Shasta Pool Supply, we've been helping Arizona hot tub owners since 1966. We've seen every water chemistry disaster you can imagine, and honestly, most of them could have been prevented with the right knowledge and the right products.

You don't need to become a chemist to enjoy crystal-clear water. You just need to follow the system we've outlined here. Alkalinity first, then pH. Test consistently. Stay ahead of problems instead of chasing them.
The next time your test strip shows numbers that don't look right, you'll know exactly what to do. More importantly, you'll have the confidence to do it right the first time.

Your hot tub should be a place to relax, not stress about chemistry. Now it can be.

Key Takeaways

Master hot tub chemistry by understanding the relationship between pH and alkalinity, then follow proper testing and adjustment procedures to maintain crystal-clear, comfortable water.

• Always adjust alkalinity first (80-120 ppm), then pH (7.2-7.8) - alkalinity acts as a buffer protecting pH from dramatic swings
• Test water 2-3 times weekly using strips or liquid kits, collecting samples from elbow-deep away from jets for accurate readings
• Use sodium bicarbonate to raise alkalinity and pH decreaser to lower it - allow 24 hours between adjustments and retesting
• Prevent imbalances by showering before use, using pre-filters when filling, and draining/refilling every 3-4 months
• Avoid chemical overuse which can damage equipment and cause skin irritation - follow dosage instructions carefully

Consistent testing and preventative maintenance will keep your hot tub water balanced, reducing the need for frequent chemical corrections and ensuring a safe, enjoyable soaking experience.

Total Alkalinity for Hot Tubs - https://www.frogproducts.com/hot-tub-school/total-alkalinity-spa/

The Unique Water Chemistry of Spas and Hot Tubs - https://taylortechnologies.com/blogs/news/the-unique-water-chemistry-of-spas-and-hot-tubs