How to Balance Your Hot Tub’s pH and Alkalinity


pH & Alkalinity play a big role in not only how safe your spa is to use but also how long it will last and how often you will have issues that need costly repairs. In this article we will cover what pH & Alkalinity are, why they matter, and how to get them into the proper ranges.

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Table of Contents

Balancing your spa’s pH and Alkalinity (also known as Total Alkalinity or TA) can be frustrating. However, it doesn’t have to be. pH and alkalinity work hand in hand, if one is off, the other will have trouble.

In spa chemistry, the words pH and Alkalinity are thrown around a lot and can be really confusing if you’re not sure what they are. In this article we will explain what they are, why they matter, and how to adjust them.

How To Balance Your Spa's pH and Alkalinity - A Quick Reference Guide

Click or Tap on the issue you are having to see the steps to resolve the issue. Further below in the article we provide more information on how to identify where your pH and Alkalinity levels are, how to add the adjustment chemicals to the spa, what pH & Alkalinity are and why they are important. We also cover several common frequently asked questions about pH and Alkalinity balancing. 

Use a pH/Alkalinity Increaser to raise both pH and Alkalinity.

Add pH/Alkalinity decreaser to lower both pH and Alkalinity.

By stubborn I mean that you have tried adjusting both with the recommended dose of pH/Alkalinity decreaser and it is either have little effect or no effect. To resolve this try the steps below.

  1. Add double the normal amount of pH/Alkalinity Decreaser.
  2. Re-Test
  3. If needed add the same amount of pH/Alkalinity Decreaser again.
  4. Repeat as needed.


What is happening is the high alkalinity must be neutralized before before pH/Alkalinity Decreaser will be able affect the pH.

  1. Add pH decreaser to lower alkalinity.
  2. Turn the pumps on high with all of the spa’s air valves open for 30 minutes and re-test

Add Alkalinity increaser to raise the Alkalinity. This will not affect the pH unless the alkalinity is increased too much.

Add pH Decreaser to lower pH. If Alkalinity drops below the ideal range add alkalinity increase to bring it back up

Try this first:

  1. Turn on the Jets/pumps with blowers and air dials turned off.
  2. Add pH Decreaser to lower the pH.
  3. Then Add Alkalinity Increaser to bring the alkalinity back into range.


It should not raise the pH above the ideal range. It is very important to have the blowers and any topside air dials turned off. Air entering water will cause a rise in the pH.

If you have “Yo-Yo” effect:

The “Yo-Yo” effect occurs when you adjust either the pH or Alkalinity and the other goes out of range. If you have this problem try one of the following two methods:

  1. Method 1:

    1. You can adjust the TA first and overshoot the 80 – 120 ppm (maybe 150 ppm).

    2. Wait 24 hours, test and adjust the pH downward (slowly, using small doses over several hours).

    3. It is very important to not use the blowers or even have any air dials open. Air entering the water will cause a rise in the pH.

  2. Method 2:

    1. Use a pH lock products (pH Balance, pH Balance Plus, pH True), which allows you to lock-in the pH without using Total Alkalinity (bicarb) as a buffering system. These products use either phosphates or borates.*

* Be careful with method 2 above if you have hard water and do not use it on swim spas or large bodies of water. These products pull calcium out of the water and if you have a high calcium hardness level it will form chunks on the surface of the water that can clog filters and cause other problems.

There are two options:

  1. Use a pH increaser product that doesn’t have any alkalinity increaser in it.
  2. Turn on the Jets with the topside air valves on and blowers on. Let the jets run for a long time. Keep re-testing and turning the jets on until in range.

Fluctuations in pH are most often caused by low alkalinity. This can be fixed with these steps:

  1. Increase the alkalinity with an alkalinity increaser (Sodium Bicarbonate) as needed. Make sure it is not a pH & alkalinity increaser product. 
  2. If pH goes out of range adjust it with the steps above.

How To Adjust Hot Tub pH

  1. Test your spa’s water with a test strip
  2. Turn on Pumps
  3. Measure out the recommended amount of pH increaser or decreaser and add it to the water
  4. Allow it to circulate for 5-10 minutes. Do not add any other chemicals in this time.
  5. Turn off the pumps
  6. Re-test with a test strip
  7. Repeat as many times as needed to reach the desired level.

Step 1 - Test The Water With A Test Strip

First test your water with a test strip and compare the strip to the chart on the back of the bottle. The target range for pH is between 7.2 & 7.8.

Test strips will vary based on what type of chemical system you are using.

If your alkalinity test strip turns purple and there is no purple color on the chart this is an indicator of too much sanitizer in your spa water.

test strip chart

Test strip example. Each brand of test strips will be different.

Step 2 - Turn The Pumps On

Turn on the spa’s pumps. Next make sure enough of the jets in the spa are turned on to circulate the water.

In most spa models, jets can be rotated and turned on and off individually.

Circulating the water helps the chemicals to disperse properly into the water.

It is best to turn on all of the pumps in the spa when adjusting pH and Alkalinity.

In most spas there are knobs that rotate that control the amount of air that can flow through the jets to enhance the massage.

Be sure to turn these air knobs off when adjusting pH and alkalinity (unless your only dealing with low pH).

Why Is It Important To Turn Off The Spas Air Valves And Blowers?

Bottom Line Up Front: More Aeration of the water and Surface Turbulence = Faster pH Rise

Many spas come with air valves on the top of their spa that allows extra air into the jets for a stronger massage. The quality of the massage is important but it’s also important to turn those off when not in use and especially when adjusting the pH and alkalinity.

In the video below from the Aquatic Facility Training & Consultants, they take a sample of water that is at a low pH of ~6.9.

They blow air into it using a fish tank aerator. This video is sped up for illustration purposes but you can see the pH change as the color on the right side of the tester changes from yellow to red. 

Raising pH with Air
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Here is the chemistry behind aeration and pH Increasing:
1. Aeration causes CO2 to outgas.
So aqueous CO2 becomes gas CO2 and leaves the water: CO2 (aq)->CO2 (gas)
2. Carbonic acid (H2CO3) in the water then creates CO2 according to this reaction: H2CO3 ->CO2 + H2O
3. Bicarbonate (HCO3–) in the water creates carbonic acid (H2CO3) according to this: HCO3– + H+->H2CO3

Net result: H+ is consumed and pH goes up — alkalinity does not increase
— pH is a measure of H+ (hydrogen ion) concentration. The less H+, the higher the pH.

Step 3 - Measure Out The Correct Amount Of Increaser/Decreaser

The math on pH can get interesting because its on a logarithmic scale. Here is an example using Brilliance for Spas pH chemicals. Each chemical brand will be slightly different.

Raising pH from a 7.3 to a 7.5 requires a half ounce per 100 gallons of spa water using Brilliance for Spas PH Increaser.

What if the starting pH is a 7.1?

7.3 and 7.1 do not seem every far off so you would normally assume that you would only need a little bit more increaser to do the job. However that’s not the case.

When going from a 7.1 or lower to a 7.5 you will add pH increaser in increments of 1.5 ounces per 100 gallons until the pH gets to 7.3 then drop down to half an ounce.

 Moral of this example: don’t stress but be very careful to read the test strip correctly and use the amount of increaser or decreaser shown on the instructions on the back of the bottle.

Measuring Cups

Freshwater pH/Alkalinity Up

Used on all Hotspring Spas Highlife, Limelight, and Hot Spot Models

Freshwater pH/Alkalinity Down

Used on all Hotspring Spas Highlife, Limelight, and Hot Spot Models

Step 4 - Allow Chemicals To Circulate

Allow the chemicals to circulate for 5-10 minutes. Do not add any other chemicals into the water at this time.

Step 5 - Turn Off Pumps

Turning the pumps off and allowing the water to settle is an important step to ensure you get an accurate reading from the test strip.

Step 6 - Test The Water Again With A Test Strip

Re-Test the pH level once the water has settled down.

Step 7 - Repeat As Needed

Repeating may be necessary if your pH levels are only slightly off.

How Do I Adjust A Spa's Alkalinity?

The target range for alkalinity is 80-120 ppm. Adjusting alkalinity varies based on the chemical system your using.

Some systems such as the Freshwater Water Care System have an alkalinity adjuster built into its pH products. In these cases you will adjust both pH and alkalinity at the same time.

However, in split systems such as the Brilliance for Spas Water Care System there is a separate product for increasing alkalinity. In either system the pH down product will also lower the alkalinity.

How to adjust alkalinity in a split system:

  1. Start up the hot tubs pumps
  2. If you need to lower the alkalinity, add pH decreaser in the amounts shown on the back of the bottle.
  3. If you need to increase the alkalinity, add total alkalinity increaser in the amount shown on the back of the bottle.
  4. Let the water circulate with the pumps on for 5-10 minutes.
  5. Turn off the pumps and let the water settle.
  6. Re-check the water with a test strip.
  7. Repeat as needed to get your water into the correct range (80-100 ppm the “ok range” shown on test strips).

Pro Tip: If your using an excessively large amount of chemicals to try to balance your alkalinity it may be a sign that the water needs to be drained and refilled.

Is There A Specific Order To Adjust pH and Alkalinity?

Yes, there very much is. It all depends on the alkalinity levels. Remember that the alkalinity if set correctly locks the pH in place and gives you the ability to control it. Preventing the pH from going up and down randomly.

If alkalinity is too high it will be very difficult to lower the pH for example. If Alkalinity is too low it will be very hard to keep the pH at a stable level.

You should always adjust the alkalinity first to the 80-100 ppm range then adjust the pH to the 7.2 to 7.8 ideal range.

How Often Should I Check pH And Alkalinity Levels?

After you have initially balanced your pH and Alkalinity you should check the levels every time you check the spa’s sanitizer levels. Checking it frequently will ensure your spa water is safe and make it easier for your sanitizer to keep your spa clean.

The frequency of testing will also depend upon how many people are using the spa and how often the spa is being used. The more people and the more frequent the use, the more often you should check the balance.

What pH And Alkalinity Product Do I Use With Chlorine, Bromine, And Salt Systems?

A common question we get asked is what pH or Alkalinity product to use with a specific sanitizer such as bromine, chlorine, and salt systems. We have developed the flow chart below to help answer this question for the two main chemical systems we carry.

Start at the top by choosing which sanitizer you use (ie. Chlorine, Bromine, or Salt System) and follow the lines and answer the questions at the diamond blocks to see which products will work best to balance your spas pH and Alkalinity.

While it is true that any pH and alkalinity product will work with any of the big three sanitizer systems (Chlorine, Bromine, Salt Sanitation), there are differences in quality of the products, how well they interact with each other, and spa manufacturers warranty requirements.

For example to maintain your warranty with a Hot Spring Highlife or Limelight Spa model you will need to use the Freshwater Chemical System. Hot Spot Spas use a combination of Spa Frog cartridges and Freshwater Chemical products.

For any other spa manufacturer we highly recommend the Brilliance for Spas line of chemicals. This line is extremely high quality and designed to give you the option of using either bromine or chlorine.

A special note on Master Spas Hot tubs. They are designed to use chlorine only. If you decide to use bromine in it you will loose the benefits of their EcoPur Mineral Filter.

pH And Alkalinity Frequently Asked Questions (FAQs)

Question: My spa has high pH and alkalinity. I have put in several ounces of pH minus with very little change. What causes this and how do I fix it?

Answer: Alkalinity locks your pH in place. Total alkalinity is the amount of “buffer’’ present in water. These buffers prevent drastic changes in pH, called “pH bounce.” When alkalinity is very high it takes a lot of pH decreaser to bring it down.

For example using the Brilliance for Spas pH decreaser (different brands will be different), lowering alkalinity from 240 PPM (Parts per Million) to the ideal range of 80 PPM in a 300 gallon spa takes 16 dry ounces. Once the Alkalinity is lowered to the correct PPM the pH will be able to be adjusted to the correct range.

Question: How does adding new water affect pH?

Answer: It depends on your local water. Some comes out balanced at pH of 7, some is high pH and some is low pH. It also depends on if you are using well water. The best way to find out how your water stands is to fill a cup from your water hose and test using a test strip. The level of alkalinity will also have an effect. Highly alkaline water will add to your spa's total alkalinity level making it harder to adjust your pH. 

Question: If I have added pH increaser by accident when I meant to add decreaser, do I just add twice as much decreaser?

Answer: Unfortunately no, it's not that simple since pH works on a logarithmic scale. This makes the math a little different than what we are commonly used to seeing. The best thing to do is let the jets run for 5-10 minutes to let it fully circulate. Then turn off the jets and re-test the water to see what the new pH reading is. Add as much as is suggested on the back of the chemical bottle to make the adjustment from the new pH reading.

What Is pH?

pH is the measure of how much hydrogen ion is present in the water. Ok, so what exactly does that mean to us? Well, the amount of hydrogen ion present determines if your water is acidic, basic, or neutral. In the chart below you can see common items and where they land on the pH Scale. A pH between 0 and 7 is considered acidic. A pH of 7 is neutral and pH between 7 and 14 is considered basic.

Hot tubs like to live between 7.2 and 7.8. The gold standard pH level for a hot tub is 7.5.

Adjusting pH can be deceiving because the pH scale is not a normal scale as we are commonly used to seeing. Think of a normal scale like a ruler where 1 inch and 2 inches are 1 unit apart. On the pH scale, for example an “8” is 10 times larger than a “7” and a “6” is 10 times smaller than a “7”. This makes the math tricky on how much pH increaser or decreaser to use. Thankfully we don’t have do the math all we have to do is measure out the recommended amount listed on the back of the bottle.

Why Is pH Important for Spas?

Excessively high and low pHs can be detrimental for the use of water. High pH causes a bitter taste, water pipes and water-using appliances become encrusted with deposits, and it depresses the effectiveness of the disinfection of chlorine, thereby causing the need for additional chlorine when pH is high. Low-pH water will corrode or dissolve metals and other substances.

Basically what the USGS is saying above is that if your spa’s water drifts too far from the ideal pH range in either direction there are two major problems that can occur:

  1. You can damage your hot tub:
    • High pH: If you have ever seen calcium buildup on a shower head then you have seen an example of the buildup they are talking about. The same thing can happen to spas.
    • Low pH: pH shifts in the acidic range can corrode metal parts. In a spa this translates to damage being caused to your heater and temperature sensors.
  2. Sanitizers like chlorine and bromine are sensitive to pH shifts. If your pH goes too far from ideal they stop working as well as they should. Which will cause you maintenance headaches and cost you a lot of money on chemicals.
    • Remember a sanitizer’s job is to keep you safe by disinfecting your spa water. Keeping your pH and sanitizer at the proper levels is really important.


In summary you need your pH to be right to ensure your hot tub has a long issue free life and the water is safe for you to get in.

What Is Alkalinity?

The buffering capacity of a water body; a measure of the ability of the water body to neutralize acids and bases and thus maintain a fairly stable pH level.

So what exactly does that mean for our hot tub? It means that if you get your pH right but not the alkalinity, you will constantly be adjusting the water’s pH. Alkalinity helps your water maintain it’s pH when other substances are added to it.

Everything has some impact on your spa’s pH. The chlorine or bromine and even the oils on your skin have some impact on pH. Without alkalinity being in the correct range each of these things and more will shift your pH.

If alkalinity is in the correct range, the alkalinity in the water will neutralize things in the water before they can cause your water’s pH to shift. This is what the USGS is talking about when they say the “buffering capacity”.


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