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. 

lake erie algae bloom, eutrophication, phosphate, orthophosphates, phosphate remover, algae prevention, types of phosphates

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

Phosphates are an 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 do to chlorine.

Strong chlorine vs. weak chlorine

Did you know there are two forms of chlorine in a swimming pool? There are. Without digging too deep in the chemistry of it, we should just cover the basics. When you put chlorine in a pool, obviously chlorine comes in contact with water (H2O). The killing form of chlorine is then formed, and it is called hypochlorous acid (HOCl). This is the type of chlorine that kills and sanitizes germs, bacteria, mold, algae, and all other things needing to be killed in the pool. It’s strong, and it is a very good sanitizer.

That said, when chlorine mixes with water, it also yields hydrochloric acid (HCl). Within seconds, a second reaction occurs, however. The hypochlorous acid (HOCl) dissociates into a hydrogen ion (H+) and hypochlorite ion (OCl-). OCl- is a weaker form of chlorine. Actually, it’s really weak. The equation looks something like this:

Cl2 + H2O → HOCl + HCl

the dissociation reaction then occurs:

HOCl ⇌ H+ + OCl


The hydrogen (H+) is the key element here. Orthophosphates interact with it, and tend to draw it away from hypochlorous acid (HOCl), which is the strong chlorine, thus creating hypochlorite ion, (OCl), the weak chlorine. Think of it like phosphates take chlorine’s strength and power away from it.

We want chlorine to keep our water safe and healthy, so it’s best to eliminate phosphates. Fortunately, we’ve got just the product. It’s called Blue PRO. It reacts with phosphates on contact, crystallizes them out of the water and flocs them to be filtered out or vacuumed. Once a year you can wipe out your phosphates from the pool, and have much better chlorine efficiency as a result. Oh, and the water clarity improves too.

A newly refilled pool was loaded with phosphates. Why?

We were recently in Michigan with our authorized dealer, Baruzzini Aquatics. A pool was being refilled when we got on site, and we were there to assist with their startup. For years, this pool had difficulties on startup with dirty filters, cloudy water, plaster damage, amongst other common problems. They decided they wanted to try our preventative, proactive pool care program.

As the water was filling up, we tested the tap water and the pool itself for the important readings: calcium hardness, alkalinity, pH, and temperature. No surprise, their pool was severely low on the LSI scale–meaning the water was pretty much guaranteed to etch the plaster–and starved of calcium. We walked the operator through our LSI calculator app and it said he needed 840 pounds of calcium! The pool was almost 300,000 gallons, and believe it or not, the number is correct. Think of it this way: calcium can either be added by hand, or the water will extract the calcium it needs until it is happily saturated. Imagine the pool sucking out 840 pounds of calcium from the plaster surface each and every summer!

Anyway, we tested for phosphates. And they were high. 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 sometimes 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…or at least that’s the theory. Phosphonic acid products are very common in the pool market too, used as stain removers and scale prevention products. Fortunately for you, our scale & metal control is non-phosphate based. But we digress.

Blue PRO phosphate remover clouded up the pool

Blue PRO, phosphate remover

See the water clouding up? That’s the phosphate remover reacting with orthophosphates in the water. The reaction would not occur if there were no phosphates in the pool.

We walked around the pool and poured in the purge dose of our concentrated phosphate remover, Blue PRO. Sure enough, it clouded up the pool instantly. Cloudiness is the expected reaction when using a good phosphate remover. The next day, the operator had his staff vacuum out the remnants of the phosphates, and now that pool’s phosphate levels will be low enough to manage the season easier. Without phosphates in the way, chemical efficiency can be unleashed.

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.

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.

swimming pool phosphates, phosphate removerAnother phosphate myth is that they cloud up the pool. This is a complicated thing, but for the most part, pool phosphates are invisible. Yes, technically they contribute to total dissolved solids (TDS), and yes they weaken chlorine’s ability to oxidize and sanitize (which can lead to cloudier water), but no, they do not directly cloud up the pool water. That said, BluePRO can help clear up water in more ways than one. It has chemical properties that go beyond simply removing phosphates, and after the cloudiness clears up (usually within 24-48 hours) the water usually looks great.

We’ll let you decide for yourself.