How to Lower Alkalinity in a Hot Tub: What Causes High Alkalinity?

So, you have set up that luxurious hot tub on a balcony, but something about your hot tub water seems a little off.  

The problem can be the high alkalinity in the hot tub water.

One common question that many hot tub owners have is – how do I get the alkalinity down in my hot tub? In fact, both excess acidity and alkalinity can cause problems for a hot tub and you need to take the right steps without delay.

Before we learn how to lower alkalinity in a hot tub, it is important to understand the basic facts about alkalinity and what causes it. 

Let’s get started.

What Is Alkalinity?

Alkalinity is the water’s ability to resist any changes in the pH level and to prevent itself from turning acidic. In other words, it is a measurement of the chemicals present in water that allows it to neutralize acids.

In natural water, the presence of acid-neutralizing bicarbonate, carbonate, and hydroxide ions causes alkalinity. Bicarbonate salts are a major cause of alkalinity and are derived from the breakdown of carbonate minerals in soil and rocks. 

The concentration of all the alkaline substances in a water sample measured together is total alkalinity. Mainly, these indicate the total concentration of bicarbonate, carbonate, and hydroxide ions.

Quite often, alkalinity is confused with the pH levels of water. Even though the two are tightly linked, they are different concepts. The pH scale ranges between 0 to 14 and measures the amount of hydrogen (acid ions) in water. On the pH scale, 7 is neutral. The numbers below 7 indicate an acidic solution. The pH of alkaline water is 8 or higher.

On the other hand, alkalinity measures the buffering capacity of water. Total alkalinity in water prevents the pH level from rising or falling rapidly. 

Total alkalinity in a water sample is measured by the process of titration. This process involves the precise addition of an acid in water till it reaches a specified pH value called the titration endpoint. 

Since it is mostly caused by carbonate minerals, alkalinity is expressed in milligrams per liter of calcium carbonate (mg/L CaCO3). At times, it is also expressed in parts per million (ppm) of calcium carbonate.

What Causes High Alkalinity in a Hot Tub

Some water sources have dissolved chemicals that raise the hot tub’s alkalinity level. This can happen when water passes through soil and rocks with a high concentration of mineral carbonates. The addition of chemicals and alkalinity accelerators like baking soda can also raise alkalinity levels. 

The other reasons can be the presence of bacteria, chemicals like soap, and body oils. The dissolved sweat, lotions, and perfumes in the water can also raise alkalinity.

In theory, the ideal range of alkalinity in water should be between 80-120 ppm. In reality, a range between 100 ppm to 150 ppm is a better choice. The range can be the same for a cold plunge tub as well.

Note, using jets and aerators in the hot tub will increase the amount of aeration and affect water chemistry. This will cause decarbonization or lower the amount of dissolved carbon dioxide in water. As a result, the water’s pH value will rise. The disrupted pH value will also affect the alkalinity.

What Happens When Alkalinity Is Too High in a Hot Tub

When the water alkalinity is too high along with a hot tub pH value of more than 8, the water can taste bitter, or more soda-like. Water with alkalinity levels higher than 120mg/l ppm can cause dry and itchy skin and also irritate the eyes. It can result in cloudy water due to calcium deposition.  The other effect is scaling due to calcium deposits on the tub surface or along the water line. 

The scale buildup also affects the pipelines, heater coils, filter, and other hot tub accessories. High alkalinity will also prevent the sanitizers like bromine and chlorine from functioning properly. This may lead to green water formation due to algae growth.

How to Decrease Alkalinity in a Hot Tub?

Before you learn how to lower alkalinity in a hot tub, it is necessary to test the tub water. You can use pool test strips to check the pH and total alkalinity of the water.

Dip a test strip into the water for a few seconds and wait till it changes color. Comparing the colors with a standard color chart provided will give you the numbers. 

One of the easiest ways to ensure low alkalinity is to add a chemical pH reducer to the tub. Make sure you use the right dose specified by the manufacturer. Note, the reducer will lower pH as well as the alkalinity of the water. So, check the pH level after addition and use a pH increaser if needed. Ideally, the pH level should be between 7.4 and 7.6.

The other effective way to lower the alkalinity and pH level in a hot tub is by adding sodium bisulfate. Other common names of sodium bisulfate are bisulfate of soda, dry acid, acid salt, sulfuric acid sodium salt, etc. Add 3 ounces per 1,000 gallons of water to lower the alkalinity by 10 ppm.

To help it mix in, add the chemical when the tub is running. Wait for 24 hours and retest the water. If needed, add more pH decreaser to bring down the total alkalinity level. In case the pH value falls below 7.2, you can use soda ash (sodium bicarbonate) to raise it.

Note, not every pool chemical is suitable for hot tub high alkalinity reduction. The harsh nature of such chemicals might damage the tub surface. Before using, check the label to find if the chemical is suitable for hot tubs.

For example, you may have heard muriatic acid being used to lower the high pH levels of pool water. However, the acid can burn the skin and damage the tub surface. So, it needs to be diluted properly and handled after wearing safety equipment like gloves, masks and eyewear.

Dosages for Lowering and Raising Alkalinity

In case the pH decreaser comes without a usage chart, you can use this chart for the right dosage.

Should pH or Alkalinity Be Adjusted First?

When the water alkalinity and pH levels are both high or both low, you can adjust them together. If the total alkalinity is low and the pH is high, raise the alkalinity first. When the total alkalinity is high and pH is low raise the pH to the normal range first. Adding a pH increaser will also raise the total alkalinity.

In truth, adjusting alkalinity without affecting pH can be tricky. It is best to make small changes to prevent large fluctuations in water chemistry. Use the test kit repeatedly to ensure that the TA levels are within the right range.

How to Lower Alkalinity in Hot Tub: Tips and Suggestions

Here are a few additional tips for dealing with the pH and alkalinity of your hot tub and proper hot tub maintenance.

• Allow the water to circulate for at least 15 minutes after adding the chemical
• To get accurate test results, wait for 24 hours after adding the chemicals to the water. 
• Always follow the manufacturer’s instructions and never mix two or more chemicals together.
• Collect the water sample in a cup and allow it to come to room temperature before testing.
• Clean the insides of your hot tub every week and wash out the filters as often as possible.

If hot tub care seems too much trouble, you can always try out a sauna. Take a look at this sauna vs hot tub article for more details.

Conclusion

There you have it. We have answered the most common queries related to hot tub water care and how to lower alkalinity in a hot tub.

Quite simply, it is essential for hot tub owners to maintain the right total alkalinity levels in the water. Balanced alkaline levels will help keep your spa water clear and clean for longer.