What Causes Alkalinity to Drop in a Hot Tub?




A hot tub is a wonderful addition to a home but you need to learn hot tub water care to keep your hot tub clean.

If you are facing problems with your hot tub’s alkalinity level you will find ways to help you with your hot tub care.

Many hot tub owners often get confused between pH and alkalinity, believing them to be the same thing. So first we will explain the difference.

What Causes Alkalinity to Drop in a Hot Tub
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Understanding total alkalinity

pH measures the actual acidity or alkalinity level of a solution. So if the pH reading was 9 then the solution would be alkaline.

Total alkalinity is a measurement of the amount of alkalinity in the hot tub water. So for example, baking soda has a pH of around 8.2. A weak solution of this would have this pH but if you added lots more baking soda the pH would still be 8.2. However, the total alkalinity would be much higher since there would be lots of baking soda in the hot tub.

An ideal alkalinity level in your hot tub maintains the pH and water chemistry equilibrium. Troubles like corrosion and much more follow when this alkaline level starts to drop.

The simple method to increase the hot tub alkalinity levels is to add an alkalinity increaser to the water. Or you can also increase the alkaline level of the water by adding baking soda (sodium bicarbonate) which, if you look at the labels, is often what is contained in more expensive alkalinity increasers anyway.

You will learn more about all this and understand why your hot tub is dropping from its ideal alkaline level in this article.

What causes low alkalinity in hot tub?

You maintain the ideal total alkaline level in your hot tubs and pools as imbalanced alkaline can cause many troubles which we will discuss later. The ideal range of total alkalinity in your hot tub lies between 80 and 120 parts per million (ppm). The alkaline levels might drop below 80 ppm due to the following reasons:

Acidic water

Acidic water is the primary cause of poor total alkalinity in a hot tub. When too many chemicals or a high dose of any chemical is added to hot tub water, it becomes acidic and alkalinity drops. When this happens, the water’s alkalinity falls below acceptable levels.

Temperature fluctuations due to rainwater

The water temperature in a hot tub is normally above 100 degrees Fahrenheit. Rainwater, on the other hand, can reach temperatures as low as 35 degrees Fahrenheit.

So, if your hot tub is outdoors and uncovered when rainfall enters your hot tub, it creates a continual rise and fall in water temperature, resulting in low total alkalinity. Otherwise, if you fill your hot tub with just rainwater, that will be more acidic than normal water as well.

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When you relax in your hot tub, you might bring in a lot of pollutants, which modifies the chemistry of the water. Sweat and probably urine are among the contaminants, as is a chemical residue that may be present in your swimsuit and body oils.

These, in turn, cause lower alkalinity in your hot tub water.

Using Epsom salts in a hot tub can also affect the alkalinity.

Excessive alkalinity reducer

Low hot tub alkalinity in the hot tub is also possible if you use too much alkalinity reducer. Products that you use as alkalinity reducers are quite acidic. If you use too many of these reducers, your hot tub may reach very low levels of alkaline.

what causes low alkalinity in hot tub

Is low alkalinity bad in a hot tub?

Low total alkalinity (that means, an alkaline level below 80 ppm) can lead to problems for both your equipment and your body.

Hot tub damage

When low total alkalinity is present, staining, etching, delamination, and cracking can possibly occur on your tub’s surface. A vinyl cover can also get deteriorated with time, becoming stiff and brittle.

Metal corrosion

Despite the fact that the majority of tubs are made of fiberglass, lower alkalinity water can still cause corrosion. This may happen on any metal surfaces in the tub, as well as within machineries like the circulation pump and filter.

Bacteria & algae buildup

Hot tub sanitizers (especially chlorine) become less effective at low alkaline levels. So we’ll need to add more to have the same sanitizing effect. Otherwise, algae and other microorganisms can flourish in your hot tub (causing green tubs).

Skin irritation

Low alkalinity causes the water to become acidic. This further irritates the people using the hot tub. It might cause itchy dry skin and also irritate your eyes and nasal passage.

pH bounce

When alkalinity is low, pH “bounces” or changes quickly. This means, you can boost the pH, but it only lasts a few hours.

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What Causes Alkalinity to Drop in a Hot Tub? 1

How to increase alkalinity in hot tub

Now how do you balance the alkalinity in a hot tub? Well, it is fairly simple. You just need to measure and add an alkalinity increaser or a base solution such as baking soda to your hot tub water. Just remember to keep the jets running.

Here is a step-by-step guide on how to raise the total alkalinity in a hot tub:

Step 1: Test the water

how to raise alkalinity in hot tub

You must also know the actual level of alkalinity in the hot tub in order to determine how much of the alkalinity increaser to add to get it up to the appropriate range. You can test the water by using digital testers, test strips, or a testing kit.

Recommended Test Strips

AquaChek 7-Way Pool and Spa Test Strips - Silver Pool Test Strips For pH, Total Chlorine, Free Chlorine, Bromine, Alkalinity, Total Hardness, and Cyanuric Acid - Water Quality Testing Kit (100 Strips)

Aquachek 7-way test strips

I use these test strips that can tell you the total chlorine/bromine, free chlorine, pH, total alkalinity, CYA and hardness levels.

Step 2: Turn the jets on

Keeping the jets on ensures that the water is being circulated well around the hot tub. This further ensures that the alkaline increaser is fully dispersed in your tub water easily and quickly.

Step 3: Measure and add products to raise alkalinity

Once the jets are on, you can add the alkalinity balancing products to your hot tub water. There are two main methods to balance alkaline levels.

Baking soda method

Can you use baking soda to increase the alkalinity in your hot tub? Of course, you can! To increase overall alkalinity levels in hot tubs, sodium bicarbonate (baking soda) is the best product to use.

Baking soda also has the advantage of being a highly safe chemical to use. Most importantly, it will have a minimal effect on the pH level of the water.

Soda ash method

To compensate for the low total alkalinity level in hot tubs, you can also use soda ash, often known as sodium carbonate. However, it also acts as a pH increaser. This means it can cause a high pH level in the water.

Both methods use the same steps, only the chemical differs. Follow these steps to raise alkalinity while using any of the above two methods.

  • Measure the amount of chemicals needed. Ideally, 1000 gallons of water need about one tablespoon of baking soda or soda ash to maintain the ideal alkaline level.
  • Add the required amount to a bucket of water.
  • Stir the mixture with a wooden spoon.
  • Pour the mixture directly into the hot tub, spreading evenly.
  • Let the water circulate for a few hours.

Step 4: Test the water again

Finally, you test the water again using a test strip or anything else. The alkaline balance in water must be restored by now. Adjust again, if alkalinity is still low, by repeating the above two steps using baking soda or soda ash again.

The chemistry of alkalinity level and pH

While alkalinity and pH are not the same, both are closely interlinked and one can affect the other. Water pH measures the quantity of hydrogen (acid ions) in water, whereas water alkalinity measures the amounts of carbonate and bicarbonate in water. You want your hot tub water to be between 7.2-7.8 on a pH scale.

In this section, you will address the following questions:

  • Can you raise alkalinity without causing a high hot tub pH level?
  • What should be adjusted first: alkalinity or pH?

Firstly, we suggest using sodium bicarbonate or baking soda instead of soda ash, as discussed above, as your alkalinity increaser. The former has a very minimal effect on the hot tub’s pH levels as compared to the latter.

You should adjust the alkalinity of the water first. Once alkaline levels are optimum, you can use muriatic acid or sodium bisulfate to bring your hot tub’s pH level back to an optimum level.

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