Every hot tub owner knows that they need to add chemicals to their how tub water but few really know what all of these chemicals do. Today, we will explain what the most common chemicals actually do.

In general, hot tub chemicals are designed to perform one of three roles:

1) Killing bacteria.
2) “Balancing” the water.
3) Improving the quality of your bathing experience.

Sanitizing Chemicals

Sanitizing chemicals are designed to kill bacteria; keeping the water clear and safe to use. Simply put, without sanitizing chemicals (either bromine or chlorine), bacteria in the hot tub water would quickly begin to multiply and cause issues with water clarity and safety.

Powdered Bromine/Chlorine

The most basic, and important, chemical that you can add to your hot tub water is powdered bromine or chlorine. These quick dissolving sanitizers can be used in small doses to sanitize the water after you use your hot tub, or in larger doses to “shock” the water.

Shock Treatments

“Shocking” is the process of burning off dead bacteria and spent sanitizers that are no longer able to do their job. Removing these particles from the water allows your sanitizers to do their jobs more efficiently. If you didn’t regularly shock your hot tub, these particles would build up in the water and you would need to use more and more sanitizer to keep the water clear and safe to use.

Bromine/Chlorine Tablets

Another way that you can sanitize your water is with bromine or chlorine tablets. Rather than dissolving instantly like powdered bromine or chlorine, these tablets are designed to dissolve slowly over the course of a few days.

Balancing Chemicals

Water balance is the relationship between different chemical measurements in your hot tub water. It is based around how water reacts with other particles. Essentially, water dissolves and holds minerals until it becomes saturated and cannot hold any more. This is known as the water’s “saturation point”.

When the water balance dips below the saturation point, it becomes corrosive. Water that is corrosive will try to saturate itself by dissolving everything it comes in contact with.

When water is above the saturation point, it becomes scale forming. It can no longer hold all of the minerals that are dissolved in it. The excess minerals will then “fall out of solution”, grouping together and forming scale on any surfaces within the water.

The goal of balancing chemicals is to get your water as close to the saturation point as possible. Each one is designed to do one of 4 things:

  • Increase Alkalinity.
  • Increase pH.
  • Decrease pH or Alkalinity.
  • Increase Calcium Hardness.

pH Increasers

pH is the measurement of how acidic or basic the water is. Hot tub water with a low pH (below 7.2) is considered acidic. Over time, acidic water will break down key components of your how tub equipment, especially metal components like the heater element. It will also cause the water to feel more “harsh” when you use the hot tub and can cause your eyes to get red and irritated.

Alkalinity Increasers

Alkalinity is essentially a “buffer” for pH. The lower the alkalinity of the water, the faster its pH levels will change. Almost everything you add to the water (including yourself) has the potential to change the pH of your hot tub water. Low alkalinity therefore makes it very difficult to maintain an acceptable pH level in your hot tub water.

pH Decreasers

Water with a pH level of 7.8 or higher is considered to be too basic. In this state, the water is beyond its saturation point and scale will begin to form on the surfaces of the hot tub. As with acidic water, basic water can also feel harsh to be in; causing dry skin and red, irritated eyes.

Along with reducing pH, pH decreasing chemicals can also be used to decrease alkalinity if added slowly over the course of a few days. Water with a high alkalinity will slowly increase in pH and will heavily resist efforts to lower its pH. In order to fix your pH problem, you therefore first have to lower its alkalinity.

Calcium Hardness Increasers

Water with a low calcium hardness is below its saturation point and will therefore try to saturate itself by drawing minerals out of the surfaces of your hot tub. This can cause things like the plumbing and jets to become brittle and prone to cracking and breaking.

Water Improvement Chemicals

Although they can perform very different functions, water improvement chemicals are all designed to improve your bathing experience in some way. These chemicals are optional and are added based on your own personal preference. There are too simply too many different water improvement chemicals available to go over all of them, so today we will focus on the most common ones.

Biofilm Removing Chemicals

“Biofilm” is a slimy layer that bacteria grow to protect themselves from things like sanitizers. This protective layer greatly decreases your sanitizer’s effectiveness as the residual in the water is constantly being used up trying to get rid of the biofilm. This means that your water will go through more sanitizer than it needs to and will turn cloudy very easily. You may also notice a visible ring at the waterline or discolouration on your filter.

Biofilm removing chemicals break up and remove biofilm buildup on the surfaces of your hot tub; allowing you to keep the water clear and safe to use with less sanitizer.


Clarifying chemicals coat your hot tub’s microfilter to help it remove fine debris that otherwise might not be removed. They can be used to give your already clear water a sparkling look or help clear cloudy water quickly.


Anti-foam chemicals are designed to lower the surface tension of the water to prevent bubbles from building up on one another to create foam. They don’t, however, fix the issue causing the foam in the first place. If you’re having consistent issues with foam you should either change the water or get your professionally tested to try and find the reason for the foam.

Stain & Scale Prevention

These chemicals coat minerals and metals like calcium and iron that are commonly found in water. By coating these particles, stain and scale prevention chemicals stop them from clumping together to form scale and stains on the surfaces of the hot tub.

Aromatherapy Oils / Crystals

Aromatherapy chemicals are designed simply to give the water a more pleasant scent. Commonly either oils or quick dissolving crystals, these chemicals typically dissipate after a couple of days and will need to be reapplied. Adding too much of these chemicals can cause some slight water quality issues, however, so be sure to stick to the recommended dosing on the bottle.

Read More: Why Should You Test Your Hot Tub Water?

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