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Phosphates and Why removing them is Important

As shared by the experts at Orenda Phosphates are often the invisible common denominator behind many pool problems.

What are phosphates and where are they coming from?

Without getting too technical, phosphates are the form of Phosphorus (P) that we most commonly find in pools. There are many different types of phosphates and phosphoric acids. There are too many variations to name, so let’s just simply refer to them all as “phosphates”.

That being said, there is something you need to know. Test kits in the swimming pool business usually only test for orthophosphates, and may not pick up the other types. But in the presence oxidizers or sunlight (….so, every swimming pool we deal with), other types of phosphates can break down and convert into orthophosphates over time. In fact, it’s not uncommon to test phosphates, and the next day has a higher level. It’s complicated, but just know that it is possible to have higher phosphate levels than your test kit shows.

Phosphates usually get into water three ways:

Chemically: there are phosphate-based chemicals like sequestering agents that are popular in the pool business to prevent scale and metal stains.

Naturally (contamination): weather like wind and rain can introduce soils and other debris from nature that contain phosphates in them. Think about plants and grass near the pool, and if the yard uses any fertilizers that could be washed into the pool during a heavy rainstorm. How about this, are you in a rural area near farmland? When the wind blows, the fertilizers they use are a huge contributor to phosphates in pools.

Tap water: Water treatment centers have been treating drinking water with phosphate-based sequestering agents. They do so to protect the infrastructure and pipes from scale formation and corrosion. And it’s a good thing they do, by the way. It’s just a problem for swimming pools that we need to be aware of. We strongly suggest testing for phosphates in your tap water to see if this is a factor in your pool.

Why should we remove phosphates?

So now that we know what phosphates are and where they come from, let’s talk about what they do and why we should remove them from our water. Phosphates are a key nutrient for microorganisms…in particular, algae.

According to renowned water chemistry expert Richard Falk, phosphates over 500 ppb can be problematic. The reason? Because phosphates allow for optimal growth and reproduction of microorganisms. Sanitization basically boils down to the growth rate of microorganisms vs. the kill rate of the sanitizer. If the growth rate exceeds the kill rate, you can get an outbreak…say, for example, an algae bloom.