Mastering Alkalinity

If you’re new to hot tubbing, it’s easy to assume alkalinity and pH are the same thing — or that they don’t matter much. Even seasoned hot tub owners sometimes struggle to understand the difference.

This guide breaks down what alkalinity really is, why it matters, and how to correct it when things go wrong

By the end, you’ll know:

How to adjust alkalinity in a hot tub
What happens when alkalinity is too low or too high
Whether chlorine affects alkalinity
How to lower alkalinity without crashing pH
Whether baking soda reduces alkalinity
Whether to adjust alkalinity or chlorine first
What causes high alkalinity in the first place

💧 What Is Alkalinity?

Total Alkalinity refers to the concentration of alkaline minerals — primarily calcium, magnesium, and bicarbonates — that buffer your pH and prevent rapid swings. Think of alkalinity as your hot tub’s shock absorber. When it’s in range, your pH stays stable, your sanitizer works properly, and your water stays clear.

🧪 Testing for Alkalinity

Alkalinity measures your water’s ability to resist pH changes.
pH measures how acidic or basic the water is.
Ideal alkalinity range: 80–120 ppm
You can test using:
Drop kits (most accurate and stable color readings)
Test strips (quick and convenient)
Local water testing at a hot tub store
Beginners should test weekly. Once you’re comfortable, twice per month is usually enough for regular use.

⚠️ Can Alkalinity Damage My Hot Tub?

Yes — both low and high alkalinity can cause real problems.

When alkalinity is too low (<80 ppm):

Corrosion of heaters, pumps, and metal components
Etching or staining of surfaces
Eye and skin irritation
Green or discolored water
Wild pH swings

When alkalinity is too low

<80 pp:

Corrosion of heaters, pumps, and metal components
Etching or staining of surfaces
Eye and skin irritation
Green or discolored water
Wild pH swings

When alkalinity is too high

>120 ppm:

Scale buildup on jets, heaters, and shell
Cloudy water
Eye and skin irritation
Elevated pH that becomes difficult to lower

🌦️ What Affects Alkalinity?

Alkalinity can drift due to:

Rainwater entering the tub
Lotions, oils, deodorants, and hair products
High‑alkalinity source water
Evaporation (minerals concentrate as water level drops)
Chemical treatments
Microbial activity
Frequent sanitizer use (chlorine and bromine can slowly lower alkalinity)

📈 High Alkalinity

Most high‑alkalinity issues come from:

High‑alkalinity fill water
Body oils and lotions
Overuse of calcium‑based chlorine
Evaporation concentrating minerals

Before adjusting:

How old is the water?

Like expired milk. If it’s older than four months, drain and refill. Old water behaves unpredictably

How to lower alkalinity

1-Sodium Bisulfate (pH Down)

2-Muriatic Acid

Use with caution

Very strong and caustic
Only for extreme cases or very hard source water
Follow label instructions carefully
When in doubt, consult a professional or consider trucked‑in water

📉 Low Alkalinity

Low alkalinity can be caused by:

Low‑alkalinity source water
Rainwater dilution
Heavy sanitizer use
Acidic lotions and oils
Microbial activity consuming alkaline compounds

How to raise alkalinity

Baking soda (sodium bicarbonate).

It raises alkalinity reliably and only slightly increases pH.

Adjustment rule

Always adjust gradually.

Small doses prevent overshooting and keep water chemistry stable.

🧭 Conclusion

Alkalinity is the foundation of balanced hot tub water. Keeping it between 80–120 ppm prevents corrosion, scaling, cloudy water, irritation, and unstable pH.

Use:

Sodium bisulfate to lower alkalinity
Baking soda to raise alkalinity

🚀 Next Steps

Test weekly (or twice monthly once experienced)
Use a drop kit for best accuracy
Maintain 80–120 ppm alkalinity
Lower high alkalinity with sodium bisulfate
Raise low alkalinity with baking soda
Make gradual adjustments
Keep up with overall maintenance (filters, cleaning, water changes)
Ask a pro if you’re unsure — water chemistry is easier with guidance

Mastering Alkalinity