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Guest Column - November 2006

Fighting Phosphates

Waterparks and Splash Play Areas

By Terry Arko

echnicians must wage a constant battle to keep algae out of their aquatic facilities. Doing so means keeping a close eye on phosphate levels. The connection between phosphates and algae growth is well documented. But what exactly are phosphates, how do they affect pool water, and how should service techs cope with them? Here's some insight.

What are phosphates?

Phosphates are biological building blocks that are formed when phosphoric acid comes in contact with certain metals. It is important to understand that phosphates exist in many different forms. Most of these come from natural sources such as rivers, lakes and oceans or mined rock. (The United States is one of the largest producers of phosphate rock.) Phosphate is termed a "pollutant" and is primarily used in soaps, detergents, shampoos and even soda pop. Other phosphate sources include fertilizers, organic debris such as leaves and bark, and some pool chemicals. Phosphate pollution in lakes and streams is caused mainly by overdevelopment, which causes extreme amounts of byproduct waste to end up in natural water systems.

The smoking gun and the bullet

Most of the phosphate in pool water enters in the form of a compound such as tri-sodium phosphate. Algae cannot use these combined phosphates as a nutrient for growth. It is not until the compounds of phosphate are broken down in the water to a free ortho-phosphate that algae can begin to thrive. Once ortho-phosphate is removed from water, it's harder for algae to obtain because it is not readily available until the phosphate compounds break down as a result of oxidation, hydrolysis or enzymatic digestion. In short, all phosphates end up as ortho-phosphate, which feeds algae. Think of it like this: Phosphate compounds are the smoking gun, but the ortho-phosphate is the bullet.


There are three vital resources that algae need to grow:

1. Nitrates
2. Phosphates
3. Carbon

Of these three, phosphate is scientifically termed as a "growth-limiting nutrient." This simply means that algae cannot thrive and flourish without phosphates. Even if nitrates and carbon are still present, algae cannot bloom without the presence of phosphate.