What is Alkalinity in a Hot Tub?
Think of alkalinity as your hot tub water’s shield. It protects the pH level from bouncing up and down like a basketball. When alkalinity is too low, your water becomes unstable—like trying to ride a bike with wobbly wheels!
Perfect alkalinity range: 80-120 ppm (parts per million)
When alkalinity drops below 80 ppm, your hot tub water becomes like a grumpy friend—unpredictable and causing problems. Let’s fix that!
Why Low Alkalinity is a Big Problem
Low alkalinity creates these headaches:
- pH keeps changing every few hours (super annoying!)
- Water looks crystal clear but feels harsh on skin
- Eyes burn and sting during soaking
- Metal parts start rusting (jets, heater, pumps)
- Chemicals don’t last long (you waste money!)
- Hot tub surface gets damaged (etching and pitting)
- Water smells like chlorine even with normal levels
Real-world example: Imagine your hot tub is like a car without shock absorbers. Every little bump (like adding chemicals or people getting in) creates a huge reaction. That’s what low alkalinity does!
Signs Your Alkalinity is Too Low
How do you spot low alkalinity? Watch for these warning signs:
✗ Test strips show below 80 ppm
✗ pH won’t stay stable (changes daily)
✗ Skin feels itchy or dry after soaking
✗ Eyes burn even though water looks clean
✗ Metal parts look corroded (rusty color)
✗ Water feels “sharp” or harsh
✗ You’re adding chemicals constantly
If you notice even 2-3 of these signs, it’s time to raise that alkalinity!
What You’ll Need (Simple Shopping List)
Good news—you probably have the main ingredient in your kitchen already!
Required Items:
- Baking soda (sodium bicarbonate) OR alkalinity increaser
- Test strips or liquid test kit
- Plastic measuring cup
- Large plastic bucket
- Long plastic spoon for stirring
- Notebook and pen
Where to buy:
- Baking soda: Any grocery store ($3-5 for 5 pounds)
- Alkalinity increaser: Pool supply stores ($12-15)
- Test kit: Hardware stores, Amazon ($10-20)
Money-saving tip: Regular baking soda from the grocery store works EXACTLY the same as expensive “alkalinity increaser” from pool stores. It’s the same chemical! Save your money.
Step-by-Step: How to Increase Alkalinity
Step 1: Test Your Water (Know Your Starting Point)
You can’t fix what you don’t measure!
Using test strips:
- Dip strip in water (elbow-deep, away from jets)
- Hold strip still for 15 seconds
- Remove and shake off excess water
- Wait 15 more seconds
- Compare colors to chart on bottle
- Write down the number
Example reading: If your strip shows 60 ppm, you need to raise it by 40 ppm (to reach 100 ppm target).
Step 2: Calculate How Much Baking Soda You Need
Here’s the super simple formula:
Easy Math:
- To raise alkalinity by 10 ppm, add 1.5 tablespoons of baking soda per 100 gallons
Real Example (400-gallon hot tub):
- Current alkalinity: 60 ppm
- Goal: 100 ppm
- Need to raise: 40 ppm
- Calculation: 40 ÷ 10 = 4, then 4 × 1.5 = 6 tablespoons per 100 gallons
- For 400 gallons: 6 × 4 = 24 tablespoons (that’s 1.5 cups)
Don’t know your hot tub size? Most home hot tubs are 300-500 gallons. Check the owner’s manual or look for a sticker on the equipment panel.
Step 3: Quick Dosage Chart (Save Time!)
Use this handy table instead of calculating:
| Hot Tub Size | Raise 20 ppm | Raise 40 ppm | Raise 60 ppm |
|---|---|---|---|
| 200 gallons | 3/4 cup | 1.5 cups | 2.25 cups |
| 300 gallons | 1 cup | 2 cups | 3 cups |
| 400 gallons | 1.5 cups | 3 cups | 4.5 cups |
| 500 gallons | 2 cups | 4 cups | 6 cups |
Pro tip: If you need to raise alkalinity by more than 40 ppm, split it into two treatments. Add half, wait 6 hours, then add the other half.
Step 4: Add Baking Soda the Safe Way
Follow these steps exactly for best results:
The Process:
- Turn on jets to full power (water must be circulating)
- Remove hot tub cover completely
- Measure baking soda carefully (use a dry measuring cup)
- Fill bucket with 1-2 gallons of hot tub water
- Add baking soda to bucket slowly while stirring
- Stir until mostly dissolved (2-3 minutes)
- Pour mixture slowly around hot tub edges (not in one spot!)
- Walk around the tub while pouring for even distribution
- Keep jets running for 30 minutes minimum
- Leave cover off for at least 1 hour
Important: Adding baking soda directly to the tub (without dissolving first) can cause temporary cloudy water and may settle on the bottom. Always pre-dissolve!
Step 5: Wait and Test Again
Patience pays off here!
- Wait 4-6 hours before testing again
- Better yet, wait 24 hours for full accuracy
- Keep jets running for 30 minutes, then turn off
- Replace cover after 1 hour
- After waiting period, retest water
Did it work? Your alkalinity should now be in the 80-120 ppm sweet spot!
Still too low? Add more baking soda using half the previous amount. Wait another 6 hours and retest.
Understanding pH vs. Alkalinity (They’re Best Friends!)
Many people get confused about these two. Here’s the simple explanation:
Alkalinity = The Bodyguard
- Protects pH from changing
- Keeps water stable
- Range: 80-120 ppm
pH = The Temperature
- Shows if water is acidic or basic
- Changes easily without alkalinity
- Range: 7.2-7.8
The relationship: When you raise alkalinity, pH usually goes up slightly too. That’s normal and expected!
What to do: Fix alkalinity FIRST, then adjust pH if needed (usually with pH decreaser).
Common Mistakes (Learn from Others!)
Mistake 1: Adding Too Much at Once
Why it’s bad: Alkalinity and pH shoot too high, creating new problems. Solution: Start with 75% of calculated amount. You can always add more, but you can’t remove it easily!
Mistake #2: Not Dissolving First
Why it’s bad: Baking soda settles on the bottom and creates cloudy water. Solution: Always pre-dissolve in a bucket before adding.
Mistake 3: Testing Too Soon
Why it’s bad: Baking soda needs 4-6 hours to fully mix and react. Solution: Be patient! Wait at least 4 hours, preferably 24 hours for accurate results.
Mistake 4: Forgetting to Run Jets
Why it’s bad: Chemicals don’t distribute evenly throughout the water. Solution: Run jets on high for 30 minutes after adding any chemical.
Mistake #5: Adjusting pH Before Alkalinity
Why it’s bad: pH won’t stay stable without proper alkalinity first. Solution: ALWAYS fix alkalinity first, then adjust pH.
What Causes Low Alkalinity?
Understanding why alkalinity drops helps prevent future problems:
Main Causes:
- Acidic chemicals (pH decreaser, shock treatments)
- Heavy rain (outdoor hot tubs—rain is slightly acidic)
- Body oils and sweat (from bathers)
- Sanitizer types (some chlorine tablets are acidic)
- Source water (your tap water might be naturally low)
- Aeration (jets and waterfalls release CO₂)
Prevention tip: Test your tap water’s alkalinity before filling your hot tub. If it’s naturally low (below 60 ppm), add baking soda immediately after filling.
How Often Should You Test Alkalinity?
Create a simple testing routine:
Testing Schedule:
- Daily users: Test every 2-3 days
- Regular users (3-4 times/week): Test twice weekly
- Weekend warriors: Test every weekend
- After heavy use: Test the next day
- After adding chemicals: Test 6 hours later
Pro tracking tip: Keep a small waterproof notebook near your hot tub. Write down:
- Date and time
- Test results (alkalinity, pH, sanitizer)
- Chemicals added and amounts
- Any problems noticed
This creates a history that helps you spot patterns and prevent problems!
Baking Soda vs. Alkalinity Increaser (Which is Better?)
Let’s settle this debate once and for all:
| Feature | Baking Soda | Alkalinity Increaser |
|---|---|---|
| Chemical name | Sodium bicarbonate | Sodium bicarbonate |
| How it works | Identical | Identical |
| Cost | $3-5 per 5 lbs | $12-18 per 5 lbs |
| Where to buy | Any grocery store | Pool supply stores |
| Purity | 99%+ pure | 99%+ pure |
| Effectiveness | Same | Same |
Bottom line: They’re the SAME chemical! Save money and buy regular baking soda from the grocery store. Pool companies just repackage it with fancy labels and charge more.
One exception: If you need to raise alkalinity WITHOUT raising pH much, look for products specifically labeled “alkalinity increaser” that contain sodium bicarbonate plus buffering agents. These are different from plain baking soda.
Maintaining Perfect Alkalinity Long-Term
Once you’ve fixed alkalinity, keep it stable with these tips:
Weekly Habits:
✓ Test water 2-3 times per week
✓ Add small amounts of baking soda as needed (1/4 cup at a time)
✓ Check pH whenever you check alkalinity
✓ Clean filters regularly (dirty filters affect chemistry)
Monthly Tasks:
✓ Deep test all water parameters
✓ Record results in your log
✓ Take water sample to pool store for professional testing
✓ Adjust chemicals based on trends
Quarterly Actions:
✓ Drain and refill hot tub (every 3-4 months)
✓ Clean entire system thoroughly
✓ Start fresh with balanced water
✓ Test source water before refilling
Troubleshooting Guide
Problem: Added baking soda but alkalinity didn’t increase much. Solution: You may have high calcium hardness. Test calcium and consider partial water drain.
Problem: Alkalinity is good but pH is too high. Solution: Use aeration (run jets with cover off for 2-4 hours) or add small amounts of pH decreaser.
Problem: Water turned cloudy after adding baking soda. Solution: Normal! Run jets for 1 hour. Cloudiness should clear in 4-6 hours. If not, check filter.
Problem: Alkalinity keeps dropping every few days. Solution: Check for acidic sanitizer use, leaks, or naturally acidic source water. May need to add baking soda weekly.
Safety First (Important!)
Baking soda is safe, but follow these guidelines:
✓ Keep dry baking soda away from children
✓ Don’t inhale powder (wear dust mask if pouring large amounts)
✓ Wash hands after handling
✓ Store in dry location (moisture makes it clump)
✓ Never mix with other chemicals directly
✓ Wait 30 minutes before entering hot tub after adding chemicals
Baking soda is non-toxic, but it can irritate eyes if powder gets in them. Rinse with water if this happens.
Quick FAQ Section
Can I use too much baking soda?
Yes! Too much raises both alkalinity AND pH too high. Always measure carefully.
How long does baking soda take to work?
It dissolves quickly but needs 4-6 hours to fully distribute and stabilize. Test after 24 hours for best accuracy.
Will baking soda make my water cloudy?
Temporarily yes, if you add it directly without dissolving. Pre-dissolving prevents this.
Can I swim right after adding baking soda?
Wait at least 30 minutes for chemicals to circulate. Better to wait 2-4 hours.
How much does it cost to fix low alkalinity?
Very cheap! A $4 box of baking soda can treat most hot tubs 3-5 times.
Your Action Plan (Start Today!)
Here’s your simple checklist:
- Test current alkalinity level
- Calculate how much to raise it
- Buy baking soda (grocery store)
- Dissolve in bucket of spa water
- Add slowly around hot tub edges
- Run jets for 30 minutes
- Wait 6 hours
- Retest and adjust if needed
Final Thoughts
Raising alkalinity in your hot tub is one of the easiest maintenance tasks you’ll do. With baking soda costing just a few dollars and the process taking less than 10 minutes of actual work, there’s no reason to let your alkalinity stay low!
Remember the golden rules:
- Test first, guess never
- Dissolve before adding
- Wait 6 hours before retesting
- Fix alkalinity before adjusting pH
- Keep a maintenance log
Your reward? Crystal-clear water that feels silky smooth, chemicals that work efficiently, equipment that lasts years longer, and a perfect hot tub experience every single time!
Take action now: Grab your test strips and check your alkalinity. If it’s below 80 ppm, you know exactly what to do. Your hot tub (and your wallet) will thank you!