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

The suggested cyanuric acid level depends on the amount of direct sunlight your pool receives and whether you use a salt chlorine generator.

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The Short, Short Version

In most cases, your best bet is to keep cyanuric acid levels between 30 and 50 ppm. Want to learn more about Cyanuric Acid? Read our article Here.

What Should Cyanuric Acid Levels Be in Pools?

The purpose of Cyanuric Acid in a pool is to protect the free chlorine from the ultraviolet rays from the sun. The two most important factors to consider in terms of balancing your cyanuric acid levels are:

  1. How much direct sunlight your pool receives.
  2. Whether or not your pool uses a salt chlorine generator

Direct sunlight received by your pool

Without any stabilizer, the sun can destroy up to 90% of the chlorine in two hours. 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.

The more direct sunlight your pool receives, the more free chlorine it will lose due to photolysis. One way to combat this is by adding more chlorine more frequently. However, this 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 as higher cyanuric acid level reduces chlorine efficacy.

Saltwater vs non-Saltwater 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 chlorine generator cells themselves. With a saltwater pool, you are not adding chlorine directly. You add salt which the salt generator processes into chlorine. You may recall that a salt generator creates sodium hypochlorite (bleach). Hypochlorite undergoes photolysis (degradation) from UV light.

Salt Chlorine generator manufacturers prefer to run at a higher level of free chlorine. This is because salt generators create chlorine continuously, so it is important to protect the chlorine that exists.

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 tubs 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 – ideally below 30 ppm, especially if your hot tub doesn’t have much exposure to UV light.

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