Pools that are suffering from algae at normal chlorine concentrations may have a cyanuric acid level that is too high relative to their chlorine content. Cyanuric acid should be between 30 and 50 ppm at normal chlorine ranges (1-4 ppm) – otherwise algae may bloom.

The Model Aquatic Health Code Committee is currently submitting change requests to the Code regarding the newly industry-accepted relationship between chlorine and cyanuric acid, and it appears that they will recommend a ratio of 30:1 Cyanuric acid:Chlorine.

That means that whatever the cyanuric acid level is, chlorine should be maintained at about 3 percent of that value.

Thus, if the cyanuric acid is 50 ppm, the chlorine should be 1.5 ppm. This ratio represents a compromise position among committee members concerning the acceptable risk of bathers contracting water borne illnesses.

For pool operators interested in preventing algae, however, there is empirical evidence that a higher percentage is warranted. Common algae seems to be kept at bay when the chlorine is maintained at 7.5 percent of the cyanuric acid. Thus, if the cyanuric acid is 50 ppm, the chlorine would be maintained at 3.75 ppm.

The most common way to reduce CYA is to simply partially drain the pool and refill. There are also some CYA reducers that also may be effective. If you’ve tried any of these products, let us know if they work.

Even with excessive cyanuric acid, some pool operators have reported decreased algae growth with the addition of a phosphate remover. Most industry standards do not include maximum phosphate levels. However, sales representatives at Orenda (manufacturer of a phosphate remover) have indicated that phosphates can become problematic if they exceed 500 ppb.

Phosphates are considered bad for pools and spas because they are a nutrient for algae. Some pools that have high phosphate concentrations have difficulty controlling algae despite maintaining normal chlorine levels.

Phosphates are typically removed from swimming pools with lanthanumbased chemicals.

Some examples include lanthanum chloride, lanthanum sulfate and lanthanum carboxylate.

Added to water, lanthanum phosphate forms a compound that is insoluble in water, and precipitates out. Experts advise that when a phosphate remover is used, the water usually appears immediately and noticeably cloudy as lanthanum phosphate, a white precipitate, is formed.

Be sure to tell pool owners that they will need to have patience with the filtration process before things begin to clear up.