How To Lower Alkalinity In A Hot Tub (and Why Too Much Alkalinity Isn't Good)

As a hot tub owner, you need to learn how to lower the alkalinity in your hot tub to maintain a balanced pH level. This post will help you understand what's going on with your water chemistry and how to lower alkalinity if it gets too high.

People enjoy relaxing in a hot tub after a long day of work. While it's a great way to unwind, hot tub owners have to avoid letting the water get too alkaline. You can run into all sorts of problems like bacteria and germ build-up and corrosion if you don't maintain your alkaline and pH levels. Here's what you need to know when your hot tub has become too alkaline and hot to deal with it.

What Happens When Alkalinity is Too High

You might notice your hot tub water turning green or becoming cloudy and foamy. That's a sign your alkaline level is too high. When your alkaline levels are up, sanitizers (chlorine or bromine) don't work very well and allow the growth of algae and bacteria. Most people recommend adding pH Decreaser or soda ash to lower alkalinity.

Measuring your hot tub's pH and alkalinity is essential to maintaining balanced water chemistry. A good pH level is between 7.4 and 7.6, while alkalinity should be kept at 80 parts per million (ppm) to 120 ppm.

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Most people associate pH level with alkalinity, but they're not actually the same thing. You don't lower alkalinity by lowering the pH level (making it more acidic) and vice versa. They're two different things, but they go hand in hand, affecting and getting affected by each other.

To keep it simple, think of alkalinity level as your buffer to keep your ph levels from going too low. Without alkaline, water in your hot tub becomes acidic too quickly. This can damage your hot tub parts like heaters and temperature sensors and corrode metal parts. Conversely, too much alkaline will prevent your sanitizers from doing their job resulting in a greenish, cloudy, or foamy hot tub.

Steps to Lower Your Hot Tub's Alkalinity

Keeping healthy water chemistry is a balancing act. You don't want your pH level and alkalinity to become too high or too low. Remember to keep your pH between 7.4 to 7.6 and your alkalinity between 80 ppm to 120 ppm.

steps to lower your hot tubs alkalinity
  1. Find out how much water the hot tub holds. Don't skip this process, or you'll end up with the wrong dose and worsen the problem. Before jumping in, make sure to measure how many gallons your hot tub can hold. It can be as simple as multiplying the length, width, and depth (length x width x depth) and multiplying the result by 7.5. This will give you an approximate number of gallons and take other measurements from there.
  2. Test the water's alkalinity. This is pretty straightforward. You just dip the test strip, pull it out after a few seconds, and compare it with the colors in the bottle to get the reading. If it goes beyond 150 ppm, you need to reduce the alkalinity right away.
  3. Add the pH decreaser to the water. Turn on the jets before adding the decreaser to ensure it gets circulated in the hot tub. You can then add a prescribed amount of pH decreaser or sodium bisulfate to the water. Refer to the instructions in the container. In most cases, 3 ounces (85 grams) added to 1000 gallons of water will drop the alkalinity by 10 ppm.
  4. Keep the jets running. Do this for 15 to 30 minutes to allow the water to absorb the decreaser fully. Turn off the jets and let the water sit for 24 hours.
  5. Re-test the water. Go back to your hot tub and recheck the alkalinity with a test strip. Your alkalinity should be lower now. An alkalinity of more than 80 ppm or less than 120ppm would be just fine. If you didn't get it right the first time, you could repeat the process.

Sometimes, no matter how much you get the levels down, you still get a high alkalinity reading. In that case, you'll have to drain, clean, and refill the hot tub. You've probably used the hot tub for quite a period of time, and the water can't handle it any longer.


Many factors can affect the alkaline level of your hot tub water. The more you use it, the more it needs to be maintained, so make it a habit to check your water chemistry once or twice a week or after the night of heavy use. Keeping the alkaline levels within desired levels means you don't have to replace water too often, and your hot tub parts are always in good working condition.