Organic vs. Inorganic Phosphates | re-post

types of phosphates, blue pro phosphate, natural pool products, phosphate remover, pool phosphates, orthophosphates, inorganic phosphates

Inorganic phosphates and organic phosphates can get confusing. This is a re-post from an article on Orenda’s website. It pertains to our audience too, so we thought we would share it, and give credit where credit is due. The original article can be found here.

Different types of phosphates

Did you know there are many different types of phosphates? In the water treatment business, most of us use “phosphates” as a general term to describe them all…but sometimes that can be misleading. There are so many types of phosphates and they react differently. In water treatment, we are most concerned about phosphates weakening chlorine through hydrogen dissociation of hypochlorous acid (HOCl), leaving behind the weak hypochlorite ion (OCl-):

HOCl  H+ + OCl

We write articles to share ideas and little-known facts. The truth about phosphates is something that needs to be clarified, because there are a lot of opinions out there—ours included. That said, this article is meant to be informative and as objective as possible.

This article is the result of extensive–and at times, boring–research. We do not pretend for a moment that we know all this detailed information by heart…nor do we expect you to. If you want to learn more, all of this chemistry information is available online. Just check our sources that we hyperlink to. As usual, we are attempting to simplify and distill the information so it is easier to understand, and applies to you, our audience.

Let’s start by dividing all types of phosphates into two main categories: organic phosphates, and inorganic phosphates.

Organic Phosphates (Organophosphates)

Organic phosphates are esters of phosphoric acid, also known as orthophosphoric acid (H3PO4). Okay…so what are esters? An ester is what you get when an organic substance (usually a hydrocarbon or alkyl) replaces a hydrogen atom in an acid. This swap (Hydrogen for an organic hydrocarbon or alkyl) makes the substance change from inorganic to organic.

Those of us who are not organic chemistry experts refer to esters as fats and oils. Natural fats and essential oils (like Omega 3) are esters of fatty acids.

According to the National Institute of Environmental Health Sciences (a division of NIH), organophosphates are a key ingredient in about half of known pesticides and nerve agents. To be clear and distinguish this from the previous statement, we are now talking about organic phosphates specifically…not other esters (fats).

Click here to see examples of organic phosphates. Fortunately, organic phosphates are not common in swimming pools.

Inorganic Phosphates

Now let’s get to the more common phosphates that we deal with in the water treatment business: inorganic phosphates.

“In biological systems, phosphorus is found as a free phosphate ion in solution and is called inorganic phosphate, to distinguish it from phosphates bound in various phosphate esters. Inorganic phosphate is generally denoted Pi and at physiological (neutral) pH primarily consists of a mixture of HPO2-4 and H2PO4 ions.” – PubChem CID 1061

We can divide inorganic phosphates into two categories: orthophosphates and condensed phosphates.


Orthophosphates are also called reactive phosphates. They are the most common in water treatment situations, as they directly contribute to the eutrophication of a body of water. Orthophosphates are found naturally in the environment and in water, but are also artificially added to fertilizers.

In swimming pools, orthophosphates are the most prevalent of all types of phosphates. These are the ones that weaken chlorineand eutrophy water (meaning they are food for plant growth…specifically algae). Usually, when people in the water treatment business talk about phosphates, they are referring to orthophosphates.

Click here to see examples of orthophosphates. You’ll notice a substance called phosphonic acid. Phosphonic acid is commonly used in drinking water treatment as a sequestering agent for metals and minerals (like calcium). Phosphonic acid is also used in pool chemicals used for stain and scale removal/prevention. It is an effective sequest, but leaves behind orthophosphates in the water.

Condensed phosphates

Condensed phosphates are types of phosphates that contain salts, metals or minerals like calcium. Within this category are pyrophosphate, metaphosphate and polyphosphate. Calcium phosphate (Ca(H2PO4)2) is a good example of a condensed phosphate. These types of phosphates are naturally occurring, but can also be synthetically combined to be used in various industries.

For the example of calcium phosphate, our bones and tooth enamel are strengthened by it. In swimming pools, calcium phosphate can harden sand and regenerative DE filter media like concrete. It can take a jackhammer to crack through it.

Types of phosphates: Conclusion

There are too many variations of phosphates to write about. It seems like any combination of P, O, H and numbers, + and – signs can be a type of phosphate. Given that we are not chemists, it gets daunting. We know. Hopefully, this article has simplified the chemistry so it is easier to understand.

As it pertains to water treatment, orthophosphates are the primary type we encounter. We recommend removing phosphates for easier water treatment, but that’s just our opinion. If you do come across organophosphates or condensed phosphates, they could give you more trouble. In pools, calcium phosphate has been known to cause severe problems in filters (hardening). In ponds and lakes (even as large as Lake Erie!), orthophosphate eutrophication can be a severe problem. 

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Orthophosphates are a primary food source for algae. And yes, bodies of water as large as Lake Erie can be affected by eutrophication.

Phosphates: The invisible problem in swimming pools

phosphates in pool water

Orthophosphates come from phosphorus, a naturally occurring element found in soil.

Phosphates are an invisible problem in swimming pools. Phosphorus, the naturally occurring element, comes in many forms…but as it pertains to pools, we care about orthophosphates. Phosphates in swimming pools have become a prevalent problem, as evidenced by the growing amount of phosphate removers sold in the U.S. pool market. But why are phosphates a problem?

First, we need to understand what phosphates are. Don’t worry, we’ve got you covered. Our parent brand–Orenda–has an article about it. Phosphorus is a key ingredient in fertilizers and is naturally occurring in the environment, yadda-yadda-yadda. Here’s the point: phosphates are an invisible problem particularly in swimming pools because of what they indirectly do to chlorine efficiency. And perhaps more importantly, because chlorine cannot remove phosphates on its own.

Kill Rate vs. Growth Rate

pool sanitization, phosphates, pool phosphates, kill rate versus growth rate, preventing algae, green poolSanitization is essentially a match between the killing rate of the sanitizer (usually chlorine) vs. the growth and reproduction rate of a given contaminant. All living organisms–including microorganisms–need phosphates to build new cells and grow.

As long as the kill rate stays ahead of the growth rate of say, algae, there will be no outbreak. But if the growth rate meets or exceeds the sanitizer’s rate of kill, an outbreak is the result. This is when pools turn green.

The conditions necessary for an algae outbreak include weakened or low levels of free available chlorine (FAC), and/or an abundance of micronutrients like phosphates. An abundance of micronutrients creates a condition in water called eutrophicationEutrophication is when there are so many nutrients that algae can take over a body of water and starve out other organisms…either by blocking their sunlight, or simply by dominating the ecosystem. Here’s a photo of Lake Erie’s algae bloom in the summer time:

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The sanitization battle needs to be won. Swimming pool health and safety depend on it. So there are two sides of the battle that can be worked on.

Boost the Kill Rate

We should do everything within reason to optimize chlorine efficiency and its killing speed. We need to get rid of as many factors that weaken chlorine as possible. We strongly recommend supplementing chlorine to handle bather waste, either with a secondary system like UV or Ozone, or with enzymes to break down and digest non-living organics.

Another important item is keeping CYA to a minimum, and preventing overstabilization. CYA dramatically slows chlorine’s kill times when the ratio of CYA to FAC gets too high. Studies show the optimal CYA levels for outdoor pools to be between 15 – 30 ppm, but going as high as 50 is acceptable too, provided you have enough FAC to maintain a decent ratio.

Slow the Growth Rate

On the other side of the battle, we can slow the growth rate by reducing phosphates. There are three main nutrients that algae needs to thrive: carbon dioxide, nitrogen, and phosphorus. CO2 is essential to pH balance, and it will be everpresent in water, so we cannot really remove it without consequences. Nitrogen will be oxidized by chlorine through the process of breakpoint chlorination, and eventually reduced down to nitrates. Nitrates cannot be further oxidized, so they are really only removed by draining water out of the pool. So that leaves us with phosphates.

Phosphates are easy and safe to remove, using BluePRO phosphate remover. It reacts on contact with phosphates, which will turn into a white cloud for a few hours (or more). When the reaction is complete, a crystalized phosphate falls out of solution to be either filtered or vacuumed out of the pool. Removing phosphates regularly helps keep the residual levels low. According to most credible sources on this topic, the goal should be to keep phosphates below 500 parts per billion (ppb).

How to phosphates get into swimming pools?

Phosphates are in our drinking water

We were filling a summer pool in Michigan that was about 300,000 gallons. Before the pool was even completely full, we tested for phosphates, and it was about 1500-2000 ppb. Since the goal is to stay below 500 ppb, we added Blue PRO, and the water clouded immediately.

Blue PRO, phosphate removerBut the question arose, “How can there be phosphates in the water? It’s literally filling up right now.” The answer is simple: the phosphates are in the tap water.

Yes, you read that correctly. See, municipalities often put phosphonic acid in their water sources because it’s used as a sequest for minerals and metals. Phosphonic acid helps protect the pipes from scale and corrosion.

Sequestering agents are often phosphate-based

Phosphonic acid products are very common in the pool market too, used as stain removers and scale prevention products. Fortunately for you, our Naturally FREE stain and scale inhibitor is not phosphate based. In fact it doesn’t even contain phosphates at all. But we digress. Just be aware that most metal removers and stain prevention products are actually phosphate-based products. And they usually will not show up on an orthophosphate test kit at first, because they are some sort of polyphosphate or condensed phosphate. But rest assured, in direct sunlight and an oxidizer like chlorine, they will break down into orthophosphates.

Phosphates are everywhere in nature…including us

Finally there is the natural introduction of phosphates from nature, and from people. When it rains, debris like pollen, leaves, pine needles, grass clippings, and soil can find their way into an outdoor pool. For indoor pools, people themselves produce phosphates that end up in the water as well. Just ask any commercial pool with a busy swim team that trains hard and sweats.

Phosphate Myths

People talk a lot about phosphates in the pool business nowadays, particularly as they pertain to algae. Yes, phosphates are a food source for algae (though not the only one), but removing phosphates does not directly kill algae. In fact, none of our products kill algae, or anything else for that matter. That’s not what Natural Pool Products do.

Phosphates also do not attack chlorine, or vice versa. This is actually part of the issue…chlorine has no way of getting rid of them. That’s why a phosphate remover like Blue PRO is necessary.

By removing phosphates, the water simply has less nutrients for algae to grow in the first place…but it can still happen in some cases. Also, if you currently have algae, using a phosphate remover may not be as effective as you hope, because algae actually stores phosphorus in its cell walls. So it needs to be killed before that phosphorus can be removed from the water.

We hope this article helps you better understand phosphates in pool water.