If the alkalinity in your hot tub or swim spa is high, it can cause cloudy water and reduce the effectiveness of your sanitizer (chlorine, bromine, etc.). So, to lower alkalinity in your hot tub, add
But why is your alkalinity high in the first place? Let’s start there and solve the problem from the beginning.
What’s the difference between your water’s pH and alkalinity? First, we have to understand that pH (potential of hydrogen) is the measurement of how acidic or basic your hot tub water is. Here’s an image to illustrate the pH scale.
Our goal is to keep the pH level balanced between the ideal range of 7.4 and 7.6. Not too acidic and not too basic.
Alkalinity, on the other hand, is the capacity of water to resist acidification (thanks Wikipedia!). But we like to think of alkalinity as pH’s bodyguard.
Hot tub pH is volatile. Any little thing that interacts with your water can cause drastic pH fluctuations. For example, when you soak in your hot tub, it could lower pH. And shocking could cause high pH. Low pH can cause corrosion. A high pH level causes scaling or cloudy water.
But when you have the right amount of alkalinity, this will take the hit before affecting your pH.
So, without alkalinity, your water’s ability to maintain pH balance would be all over the place. Alkalinity and pH are related, but they are not the same.
Unlike pH, total alkalinity is measured in parts per million or ppm for short. Most resources tell you to keep it between 80-120 ppm. However, we recommend keeping your hot tub alkalinity level between 100-150 ppm to give yourself more room. We have an article all about hot tub water chemistry if you’re interested in learning more.
Tests for 7 important chemistries in seconds: Total Hardness, Total Chlorine, Total Bromine, Free Chlorine, pH, Total Alkalinity, and Cyanuric Acid.
NOTE: If you’re dealing with low alkalinity, we have a guide on how to raise alkalinity in a hot tub here.
To be fair, high alkalinity is not a common issue in hot tubs. Mainly because most owners drain and clean their hot tubs every 3-4 months to keep things from building up.
That said, there are a few main causes of high alkalinity in a hot tub:
The main thing that can happen is it renders your sanitizer (chlorine, bromine, etc.) useless. That can cause green water and bacteria to grow, making the hot tub unsafe to soak in. Secondly, it can cause a calcium scale build-up, which will make your hot tub work twice as hard to heat up.
All of this puts hot tub soakers at risk for skin issues like hot tub folliculitis. Plus, it puts you (the hot tub owner) at risk for empty wallet syndrome by replacing heaters and adding more sanitizing chemicals.
The easiest way to lower alkalinity in your hot tub is by adding a
Before you add
Lower your hot tub pH with a pH decreaser. High pH can damage your hot tub equipment, cause cloudy water, and irritate eyes and skin.
No. White vinegar (or any other type of vinegar) does not lower alkalinity. It will only lower the pH in your hot tub.
Hopefully, that answered a lot of your questions about lowering hot tub alkalinity and how to prevent it from being so high in the first place. Here are a few more tips for dealing with both pH and alkalinity:
I found the questions hot tub owners ask the most about lower alkalinity and answered them here.
No. Baking soda raises alkalinity because the main active ingredient is sodium bicarbonate. If you’re looking to lower it, reach for a
Shocking your pool usually doesn’t affect alkalinity much. But chlorine shock can actually raise your pH. That’s why I recommend using a non-chlorine shock for chlorine and bromine hot tubs
Yes. Over time, as you use the hot tub, the alkalinity level could decrease. That said, it can also increase. If your alkalinity is high, I wouldn’t wait. I would add
Soaking in high alkalinity water won’t harm you, but it can be uncomfortable on your skin. I would not soak in hot tub water that’s got a high alkalinity reading. It can also make the water cloudy and potentially harm your hot tub components.
Lowering alkalinity without affecting pH is tricky. You’ll need to add a
I would NOT do that. While we sometimes recommend adding it to a pool, it’s too much to add to a hot tub. I recommend just sticking to using a
Lower your hot tub pH with a pH decreaser. High pH can damage your hot tub equipment, cause cloudy water, and irritate eyes and skin.
Matt is the founder of Swim University. He's been in the pool industry since 1993. His mission is to make pool care easy for everyone. Each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
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