Is High or Low Alkalinity in a Hot Tub Dangerous?

If your water test has come back with an alkalinity imbalance, you might be tempted to ignore the problem, and you may even think about taking a soak. But is it safe to do so?

When the alkalinity is too high, it results in sanitizers being less effective, in serious health conditions, in a limescale build-up, and in cloudy water. Low alkalinity results in pH fluctuations, damage to the hot tub’s components, green water, and irritation to bathers.

Unfortunately, an alkalinity imbalance has many knock-on effects, so it needs addressing right away. Let’s take a closer look at the potential damage that’s caused by ignoring the issue.

What happens if alkalinity is too high?

The pH level rises

If the alkalinity level in your hot tub rises, the pH level will also rise. Therefore, you’ll have to lower both the alkalinity level and the pH level. This process can be time-consuming since you have to do several rounds of water testing to get the proper balance of water levels.

Sanitizer effectiveness reduces

Another effect of high alkalinity levels in your hot tub is that it reduces the effectiveness of the chlorine or bromine sanitizers in your spa. 

This decrease in effectiveness is majorly caused by the high pH levels and would result in spending more money on chemicals in an attempt to increase sanitizing power.

Because the sanitizers are less effective, harmful bacteria and algae blooms would start to build up in the hot tub, causing the spa water to turn green quickly.

Your hot tub’s pH should remain between 7.4–7.6. At a pH of 8.0, chlorine is about 20 percent effective in water. At pH levels of 8.5 or higher, chlorine’s effectiveness reduces to under 10 percent. Adding more chlorine or shocking the hot tub will not lower the alkalinity.

Health issues

High alkalinity levels can also be harmful to your health. A hot tub with an alkalinity imbalance can cause allergic reactions, stomach cramps, gastrointestinal upsets, nausea, breathing difficulties, and vomiting.  Other health issues include burning eyes, itchy skin, and nose and throat irritation.

Limescale build-up

A rise in pH will result in high levels of calcium. Once this happens, you’ll notice scales floating on the water’s surface. Limescale deposits can cause significant damage to your hot tub components like the heater and pump.

The scale can also clog the hot tub’s jets and filter. This will cause the flow of water to decrease. It will also increase the time it takes for your hot tub to heat up. 

Cloudy water 

Another effect of high alkalinity levels is that it turns the spa water cloudy. This is usually caused by the excess calcium in the spa.

What causes high alkalinity?

Adding too much baking soda or soda ash (alkalinity increaser) to your hot tub water can lead to high alkalinity levels. Adding too many chemicals can also cause alkalinity imbalance. 

Shocking your hot tub is another cause of high alkalinity. When you add liquid chlorine (sodium hypochlorite) to your hot tub, it leaves behind excess hydroxides, which can cause alkalinity to rise. This is why you should only use this chemical for swimming pools, never in hot tubs.

Bodily fluids and body products can also cause your alkalinity to rise. Taking a quick shower before entering the spa is a good way to prevent pollutants from entering the water. A quick shower would help rinse off the contaminants from your body. 

Rinsing your body before entering the hot tub can be helpful, but it doesn’t stop bacteria from entering the spa water. This is why you need to add chemicals that can kill bacteria. 

However, when you keep adding chemicals, they lose their effectiveness over time. This is why you should drain your spa water every 3-4 months to keep things fresh.

Another thing that can cause high alkalinity is your water supplier. You may live in an area where the water source has a naturally high alkalinity level. Therefore, anytime you refill your hot tub, you’re going to experience high alkalinity levels in the water.

What happens if alkalinity is too low?

pH levels will fluctuate

When the alkalinity level of your hot tub water is too low, the pH level will fluctuate rapidly. The water can abruptly change from acidic to alkaline and vice versa. This is also known as pH bounce, and it occurs when there isn’t enough pH buffer in the water.

Low alkalinity is worse than high alkalinity. It can reduce the pH level of the spa water, causing it to become acidic. Acidic water is harmful to both bathers and the hot tub.

Irritation to bathers

Low alkalinity can cause dry and itchy skin. It can also irritate the eyes and nasal passages. It can even cause respiratory problems for some people. 

Green water

Low-alkaline water cannot balance the number of phosphates in the water. Since the spa water is not neutrally balanced, algae blooms begin to grow in the hot tub. This causes the water to turn green.

Damages to hot tub components

Low-alkaline water is acidic water, and acidic water is corrosive. The high temperatures and rapid flow rate in hot tubs make the acidic water even more corrosive. 

This corrosive water can cause damage to pump seals, heating elements, pipes, heaters, and other metal components in the water handling system. Acidic water can also cause staining, cracking, etching, pitting, and delamination of the spa shell.

What causes low alkalinity?

Why is my hot tub alkalinity always low?

One of the causes of low alkalinity in your hot tub is the contaminants from your body. Every time you use your spa, millions of bacteria are introduced into the water from your body. 

Pollutants like body oils, personal care products, urine, or sweat can alter the water chemistry. This is why it’s important to shower before entering the spa.

Overusing alkalinity-lowering products (muriatic acid or sodium bisulfate) can also lead to low alkalinity. Therefore, when treating your spa water with an alkalinity decreaser, ensure you don’t add excess amounts.

If you’re experiencing low alkalinity levels, it could be because you use chlorine tablets (trichlor) wrongly. Chlorine tablets are highly acidic (2.9 pH). They can reduce alkalinity and pH levels faster than pH-neutral products like chlorine granules. 

Therefore, if you’re using chlorine tablets, ensure you balance your water regularly.

Rainfall is another cause of low alkalinity levels in your spa. As rain falls, it combines with air pollutants which make the rain droplets acidic. Ensure you cover your tub during a heavy downpour.

Joshua Milton

Joshua Milton is a seasoned hot tub enthusiast. With many years of experience in the industry, he offers valuable insights on hot tub maintenance, health benefits, and relaxation techniques.

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