How To Raise Alkalinity In A Hot Tub If It Gets Too Low

This article describes a simple, inexpensive method of raising alkalinity in a hot tub and gives the most common reasons why alkaline levels in your hot tub drop.

A hot tub is a great place to relax and unwind, but if the alkalinity in a hot tub gets too low, it can become a health issue and cause many problems to your hot tub parts. You may find yourself wondering how to raise alkalinity in a hot tub. This article will explain the most common reasons why alkalinity levels in a hot tub drop and how you can solve these problems.

What is Alkalinity?

In simple terms, alkalinity determines the alkaline level in your hot tub water. The ideal range falls between 80 and 120 parts per million (ppm). Your alkaline levels are either too low or too high outside those ranges.

Total alkalinity (TA) keeps your hot tub from becoming too acidic. If it gets way too low, your pH levels could spike very quickly. Think of it as your buffer against wild fluctuations in the water chemistry. You don't want it to go too high either; otherwise, your sanitizers (chlorine or bromine) would stop working.

What Causes Alkalinity to Drop?

Each time we use our hot tubs, we bring in tons of pollutants like body oil, sweat, detergents from bathing suits, etc. This can cause drastic changes in your hot tub's water chemistry.

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Rainwater can also make your hot tub alkalinity go down, especially after a heavy downpour. Unlike tap water, rainwater has a natural tendency to become acidic. We recommend putting your hot tub cover on to protect it from pollutants and contaminants.

Another cause of low alkaline levels is the sanitizers themselves, particularly chlorine tablets, because of their low pH levels. To achieve ideal water chemistry, you need to balance alkalinity and pH levels.

2 Methods to Bring the Alkaline Levels Up

There are two ways you can bring the alkaline levels back up. Both methods work, and they're surprisingly easy to do. You don't have to buy expensive chemicals, and you might already have one at home.

Method 1: Baking Soda

Most alkalinity increasers are just basically baking soda in a fancy-looking bottle, so if you have one at home, you don't need to go to the hardware or grocery store. Its chemical name is sodium bicarbonate, and it works extremely well in bringing your hot tub's alkalinity back up. So here's how it's done.

baking soda

First, you need to know how many gallons of water your hot tub holds. You can do this by multiplying the length, width, and depth (feet) and multiplying the result by 7.5. To raise alkalinity, use one tablespoon of baking soda per 100 gallons. Hence, if your hot tub holds 600 gallons, you'll need six tablespoons of baking soda.

Dissolve baking soda into a bucket of water and pour it into the hot tub. Turn on the jets and let it circulate for about 6 hours. Recheck your hot tub's alkalinity using test strips and repeat the process if needed. Your goal is to bring it up to the 80 to 120 ppm range.

Method 2: Soda Ash

It's the same process as Method 1, but you're using soda ash instead of baking soda. Its chemical name is sodium carbonate, and it works just like baking soda but is more potent. However, unlike baking soda, it will also lower the hot tub's pH level. We recommend only using this method if the alkalinity in your hot tub has dropped significantly. Otherwise, just go with your regular baking soda.


Same with baking soda, you need one tablespoon of soda ash for every 100 gallons of water. Dissolve it in a bucket of water before pouring it into the hot tub. Let it circulate for 6 hours and re-test the alkaline levels. Repeat if necessary. Note: you might overshoot the 120 ppm range since most of it is just trial-and-error. You can bring it down using an alkaline reducer such as sodium bisulfate.


Make it a habit to test the alkaline levels of your hot tub before it gets too low. There's a high risk of corrosion in your hot tub parts and causing skin irritation if your hot tub becomes too acidic, and you spend more money in the process. Prevention is key. Spending a few bucks on test strips and a few minutes of your time testing your hot tub's alkaline levels can go a long way.