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.