Guide To Lowering Alkalinity In A Hot Tub

When maintaining a hot tub, there are a few things owners have to consider—including the water’s pH and alkalinity. The pH of the water should sit at around 7.2-7.8, and the alkalinity should be about 80-120 ppm (though slightly higher isn’t usually cause for concern). Anything significantly higher needs action.

If the alkalinity is too high, it can disrupt the hot tub’s cleaning process and equipment. You should test the pH and alkalinity around once a manage these levels using pH and alkalinity adjustment products. To add alkalinity, you can simply add baking soda. To lower it, drain water. 

Its important that everything in the water remains balanced so you and others can enjoy your hot tub without worrying. So now, let’s take a closer look at alkalinity in hot tubs, from what this means to how to keep it at a reasonable level that will save your hot tub equipment.

Alkalinity in Hot Tubs: What is it?

Spa Jacuzzi Hot tub water quality testing

The pH of your hot tub determines how acidic or basic the water is. The more alkaline the water is, the more resistance it has to becoming acidic.

Although alkalinity and pH are very closely related, they’re not quite the same. While you want the pH to be between 7.2-7.8 (with 7.4-7.6 being the ideal range), the alkalinity should be around 80-120 ppm.

Why is Alkalinity Important in Hot Tubs?

Although it may sound like a good thing for hot tub water to veer far away from becoming acidic, it mustn’t stray too far in the opposite direction, or it will interfere with how it filters out water and balances the chemicals. Hence, we don’t want the alkalinity to become too high.

What Happens if the Alkalinity Gets Too High?

A few things can happen if your alkalinity gets too high, so keeping an eye out for these signs is crucial.

Cloudy Water

The first is that you may notice the water becoming cloudy. This is only a cosmetic issue, so there’s no need to worry if you see this, but it is a sign you need to change the alkalinity in the water (and keep an eye out for other, more severe signs).

Calcium Build-up

You may notice a calcium build-up in the water and cling to the equipment. This is where it starts to get dangerous, as this can interfere with how that equipment works and cause problems. It may end up blocking the jetlines and filters.

Chlorine Balance is Off

Your chlorine chemical balance may also be affected. Chlorine is essential for hot tub water because it kills off algae and bacteria, so it’s crucial to monitor the level. If there’s high alkalinity, the chlorine will die much quicker, and you’ll need to top it up more.

The Effects

The result is that it can cause problems for people getting in the water. For example, you may notice plastic goggles eroding and swimwear fading as the water eats away at these substances.

Worse still, it can interfere with health. For example, it can cause skin irritation and clog up nasal passages, making people feel stuffy. This can be particularly dangerous for children and those with pre-existing respiratory issues.

How to Fix the Chlorine Balance

If the alkalinity has thrown off your chlorine balance, you’ll need to fix that too. You should fix the alkalinity first, but then you can go ahead and check the chlorine.

Hot tubs should have around 3-5 mg per liter, so if there’s any less, add more. You can get chlorine in liquid form or tablets, but the tablets are usually better to use because they have a stabilizer and are pre-measured. Liquid is also acceptable, but it may burn up more quickly if your hot tub is in the sun.

How to Lower Alkalinity in a Hot Tub 

If you’ve noticed that the alkalinity is too high, then it’s time to bring it back down. You can either use sodium bisulfate or muriatic acid to bring it to an average level.

Using Sodium Bisulfate Products

  1. Make sure you test the water before going ahead, as this will tell you the total amount of alkalinity in the water.
  1. You should follow the bottle’s instructions to see how much to add. If you have pure sodium bisulfate (on Amazon), you should use around 3.5 ounces to lower a 1000-gallon tub by ten ppm. Do calculations to find out how much you, specifically, should add.
  1. Take some water out of the tub in a bucket and mix the correct amount of solution with it thoroughly, then pour it back into the tub.
  1. Allow it an hour or so to circulate through the system, and then re-test the water to see if you need to add more.

Using Muriatic Acid

Using muriatic acid is another effective way, but you should take extreme care when using it. Muriatic acid, also known as hydrochloric acid, can burn the skin to the touch, so take extra care and use gloves and goggles.

  1. First, turn off the hot tub pump, so the water is no longer circulating.
  1. Then, test the water just as you would for sodium bisulfate to get the current level.
  1. Check the bottle to see how much you need to add, and then put it with some water from the hot tub before pouring it back on. Don’t let the pumps run; this will work better with still water.
  1. Give it an hour or so, turn the pumps back on, and let the water circulate.
  1. Test the levels to see if the alkalinity is back to the desired amount. If it’s not, you can repeat the process, using less muriatic acid if you only need to lower it a little more. Of course, less is always better because you can add more, but you can’t remove what you’ve already added.

Do not let children or pets near the hot tub during this time, and ensure it’s fully circulated into the water before getting back in.

How to Lower Alkalinity in a Hot Tub Naturally 

If you don’t want to use these chemicals to lower the alkalinity or simply don’t have them on hand, you can also use vinegar (though it will take longer and use more).

Start by adding four cups of vinegar to the water and letting it circulate via the pool pumps. Then, test the alkalinity again and keep adding vinegar and testing until you reach the desired alkalinity level, ensuring you leave an hour between tests so the vinegar has enough time to settle into the water.

Are Alkalinity and pH the Same Thing?

Although alkalinity and pH are closely related, they are not the same. Alkalinity is a different measurement from the pH number of the water.

How to Bring the pH Back Up

Firstly, you should be testing the pH of the water frequently, using test strips (on Amazon). If it falls below 7.2, it’s time to bring it back up.

There are specialized products (on Amazon) to bring the pH back up, but otherwise, you would use the same products you do to bring the alkalinity up.

What Happens if the Alkalinity is Too Low?

Hot Tub Water Quality Check by Using Chemical Testing Kit

As well as being too high, the alkalinity being low can also be a problem—in fact, it often presents a much more severe problem than high alkalinity.

The most common sign that the water is too acidic is that people are deeply irritated when entering it and can even break out in rashes or have respiratory issues more serious than what high alkalinity might cause.

It can also cause staining and cracking in the tub and damage equipment, so if you test the alkalinity and find it’s actually too low, it’s vital to act as soon as possible.

You can use sodium bicarbonate, an alkaline chemical, to raise the alkalinity. There are also specific products for this, but these are almost always made with this or baking soda (on Amazon), which is also a natural product that can do the job.


Overall, both alkalinity that’s too high or too low can be a severe problem for your hot tub, and it’s important to test frequently and look out for the signs. At best, leaving it for too long can be a time-consuming cleaning job; worse, it can damage the hot tub or even be dangerous.

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