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Phosphates in pool water

May 23, 2016


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Has anyone ever told you about phosphates in pool water? Do you know what they are, or what they do to pool chemistry? For most people, the answer is no...including many pool professionals who have not had to fight phosphates before. While Orenda has done extensive R&D to formulate their eco-friendly PR-10,000 phosphate remover, this article is just a summary of information from multiple outside sources, simplified for you. We have another article that goes more in depth about different types of phosphates here.

What are phosphates?

We are talking about compounds that contain phosphorus. When compared to other topics in pools, there is surprisingly little scientific detail about phosphates available online. But there are some reliable sources. According to the Water Research Center:

“Phosphates exist in three forms: orthophosphate, metaphosphate (or polyphosphate) and organically bound phosphate. Each compound contains phosphorous in a different chemical arrangement. These forms of phosphate occur in living and decaying plant and animal remains, as free ions or weakly chemically bounded in aqueous systems, chemically bonded to sediments and soils, or as mineralized compounds in soil, rocks, and sediments.”


inorganic phosphates, fertilizer phosphates, pool phosphates, phosphates, phosphate remover, eutrophication Fertilizers contain phosphates. With rain and wind, these phosphates often find their way into swimming pools.


Translation: phosphates are found in soil, which is a combination of broken down rocks (with phosphorus in them), and decaying plant and animal remains. They are prevalent in fertilizers, as well as other pool chemicals (such as metal sequests, which are actually phosphate based).

Phosphates are not always a bad thing. Remember the 2015 water crisis in Flint, Michigan? Well it turns out that one of the ways the local health department is mitigating the problem is by adding phosphates to the water, so more scale develops to coat the inside of the lead pipes, thus reducing lead in the water.

Flint is not alone, as many other localities add phosphates to protect their water pipes from internal corrosion. As a result, if your pool is filled by public water, there’s a good chance you have phosphonic acid in your pool from the start. According to one source, however, less than 20% of US municipalities have a significant level in their tap water.


pool algae, green pool, orenda pool, orenda, phosphate remover, pr10000 Phosphates are food for algae, but removing phosphates doesn't necessarily kill algae.


Since phosphates are natural in the ecosystem, they will inevitably get into your pool water in many ways other than tap water: rain water/ground runoff, leaves in the pool, etc. For outdoor pools, these sources are unavoidable. Despite being a nuisance, phosphates are rarely discussed in CPO courses, and to many experts, they are not even regarded as a problem. Algae is the problem everyone talks about.

We respectfully disagree.

High Phosphate Symptoms

The little research available seems to suggest that phosphates do not affect water clarity much, if at all. In fact, many experts argue that phosphates are a non-issue if your pool is properly balanced. They say that because the most common symptom is algae; a symptom that can be killed with chlorine and its supporting chemicals in a balanced pool.

But it’s odd, because that doesn’t always mean algae will grow. Testing is the only way to know for sure. As it pertains to algae, subsequent symptoms include greenish water, stains in the white-coat surface, more scum on the scum line, and greasy, grimy filter sand.

What’s the big deal? Do phosphates even matter in pool water?

Most of the research suggests inorganic phosphates are not harmful to people; which is good news, considering local governments add phosphonic acid to our drinking water (as a scale and metal sequest). So why even worry about them?


All articles keep coming back to algae. Yes, we get it. Algae is a nuisance and phosphates are its food. But will removing phosphates prevent algae? The science is still uncertain, as there are studies arguing both sides. What they all seem to agree upon is that plant growth (like algae) requires certain elements…and phosphorous is only one. Algae also needs nitrogen and potassium, for example. Killing algae is the job of chlorine…specifically free chlorine. If the chlorine is bogged down fighting other things—say, organic waste, for example—it may not have enough strength to totally kill the algae.

Either way, phosphorous in all forms contribute to the eutrophication of water. It is especially a problem for lakes and ponds...but swimming pools can have eutrophication issues as well.

Operating costs

More chemicals means more costs, regardless of which chemicals you’re using. A healthy, balanced pool under regular maintenance may not have the need to address phosphates often, if at all. Phosphate removal products can get expensive if you use them regularly, so it all depends on the situation you’re in. If the pool is in a constant struggle, it’s okay to ask for help! Each pool is unique and should be treated as such.

Are phosphates worth testing for?

pr-10000, pr10000, orenda pr, orenda phosphate, phosphate remover, best phosphate remover, orthophosphatesYes, knowledge is power. Phosphate test kits readily available in pool supply stores, and they’re inexpensive and easy to use. It can’t hurt to know what you’re up against. Levels under 250ppb are considered low. 250-500ppb should be considered when balancing the rest of the chemicals, and 500ppb+ should be addressed directly. It is good practice to have your pool’s phosphate levels checked at least monthly.

It may be in a pool owner/operator’s best interest to start the pool season with a treatment of PR-10,000, and end the season with it as well. Depending on the variables of your area, those two treatments alone may be plenty. If not, follow the dosing calculator on our website.

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