What is the right Cyanuric Acid Level for Swimming Pools and Hot Tubs?

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In most cases, your best bet is to keep cyanuric acid levels between 30 and 50 parts per million (ppm).

What Should Cyanuric Acid Levels in Swimming Pools

The two most important factors to consider when balancing your cyanuric acid levels are:

  1. Whether your pool uses a salt water generator
  2. How much direct sunlight your pool receives.

We will discuss the former in the next section, so feel free to skip ahead if you use a salt water generator to sanitize your pool.
The energy contained in UV light from the sun causes the hypochlorous acid and hypochlorite ions formed from the reaction of chlorine and water to break apart in a process called photolysis. Learn more in our article What is Cyanuric Acid?

If your pool receives more direct sunlight, more free chlorine will be lost due to photolysis. One way to combat this is by adding more chlorine, more frequently. However, that is both expensive and time consuming. A better approach is to keep your cyanuric acid levels slightly elevated between 60 and 80 ppm. This also means will want to keep your free chlorine levels elevated between 4 and 5 ppm.

What Should Cyanuric Acid Levels in Salt Water Swimming Pools

Saltwater pool manufacturers recommend maintaining cyanuric acid levels around 60-80 ppm. This is a bit higher than the 30-50 ppm range recommended for non-saltwater pools. And if you live in an area where your pool gets a lot of direct sunlight, you may even consider bumping your cyanuric acid up to 80-100 ppm.
The reason saltwater pools demand elevated cyanuric acid levels has to do with the output of the salt cells, themselves. With a saltwater pool, you are not adding chlorine directly. You are adding salt which gets processed into chlorine via a saltwater [chlorine] generator.
You may recall that salt is sodium hypochlorite. Remember that hypochlorite undergoes photolysis from UV light. So, saltwater pools are effectively taxed double by sunlight. First, when the salt is added to the pool. Second, after chlorine is generated from the salt. That is why saltwater pools demand a higher cyanuric acid level between 60 and 80 ppm.

What Should Cyanuric Acid Levels Be in Hot Tubs?

Unlike swimming pools, the concern with hot tubs is that cyanuric acid is too high. On one hand, cyanuric acid protects free chlorine from evaporating from exposure to UV light. On the other hand, cyanuric acid slows down the speed at which free chlorine sanitizes water.
This buffering effect is inconsequential in swimming pools. However, hot tubs tend to have a much higher concentration of contaminants because they have a much higher concentration of swimmers – who also perspire more due to the temperature of the water. If cyanuric acid levels get too high, they can render free chlorine ineffective against sanitizing pseudomonas aeruginosa bacteria (hot tub itch).
The most common way hot tub owners increase cyanuric acid is by adding stable chlorine to their hot tub (e.g. dichlor or trichlor). These chlorine solutions include stabilizer in them, which means cyanuric acid is added every time chlorine is added. We recommend using a spa-specific chlorine to keep cyanuric acid levels as low as possible – around 30 ppm.

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