So what exactly are phosphates? In general, the compound that is referred to as “phosphate” is orthophosphate. It is simply a phosphorous atom surrounded by four oxygen atoms, PO4-3. It can exist as it is written (an ionic species dissolved in solution) or it can be attached to another molecule such as a protein. Phosphates come from a variety of different sources. These include fertilizer, industrial discharge, swimmer waste, detergents and chemicals used to treat corrosion in drinking water – just to name a few. Phosphorous is actually the eleventh-most abundant mineral in the earth’s crust. So basically, it’s everywhere in many different forms. It is an essential nutrient for all life – both plant and animal.
So the question becomes “Does orthophosphate contribute to chlorine demand?” The answer to this question is no. In lab studies, we have not been able to increase chlorine demand by adding additional phosphate to water samples.
You may remember that all atoms have what is referred to as a preferred oxidation state. This is simply a number that is assigned to a particular atom based on its chemical properties. For example, the preferred oxidation number for chlorine is -1. The preferred oxidation number for phosphorous is +5. Atoms in an oxidation state that is not preferred are very reactive, while atoms in their preferred oxidation state are stable and are much less reactive.
In hypochlorous acid (HOCl), chlorine is in an oxidation state of +1. Because chlorine is constantly trying to reach its preferred state of -1, it is very reactive. This is why hypochlorous acid is such a great oxidizer. When hypochlorous acid oxidizes other material, the chlorine atom reaches its preferred oxidation state of -1.
In the orthophosphate molecule, the phosphorous atom is already in its most preferred oxidation state of +5. Therefore orthophosphate is not likely to participate in these types of chemical reactions with hypochlorous acid. If material does not react with hypochlorous acid then it does not contribute to chlorine demand. This theory has proven true in lab testing as mentioned above.
So if orthophosphate does not contribute to chlorine demand, does it contribute to algae growth? The answer to this question is simple. In a properly maintained pool environment (which includes the recommended level of sanitizer) phosphate does not play a role in the growth of algae.
All plants, including algae, require several essential nutrients for growth. These include hydrogen, oxygen, carbon, nitrogen and phosphorous. The addition of these nutrients to an environment such as a lake or pond may increase algae growth and disrupt the balance of the ecosystem. The EPA puts limits for discharge of nutrient containing water into lakes and streams so as not to upset this balance. However, a pool environment is completely different so the same limits do not apply. A pool environment includes filtration as well as the use of sanitizers and algicides which would be toxic to aquatic life.
There are some opinions that using a phosphate remover will stop or at least inhibit algae growth in pool water as well as assist with chlorine demand treatment. There are currently no phosphate remover products that are EPA registered as algae killers (algicides) or algae inhibitors (algistats), therefore none of these products can make that claim. The reason is that no supporting data exists. It is also important to note that phosphate removers only remove orthophosphate and not all sources of phosphorous (such as phosphonates, polyphosphates and phospholipids, etc.).
Phosphate removers may act as a floccing agent to remove other material from the water. Physically removing some contaminants is always an option for assisting with chlorine demand treatment and can be achieved with any number of floc-based products. Using a product designed specifically for this function will deliver better results.
But would the removal of orthophosphate assist with algae treatment?
The answer is NO. There are several reasons for this.
1. It was stated earlier that phosphorous is essential for all life forms both plant and animal. Orthophosphate is a readily available source of phosphorous for plants, including algae. However, it is not the only source of phosphorous. If orthophosphate becomes unavailable as a source of phosphorous, then the algae will simply find it from another source. Remember that these products only remove orthophosphate and not all phosphorous containing compounds. Additionally, phosphate removers cannot remove phosphate levels down to zero. There is evidence to suggest that some types of algae will in fact take up extra phosphorous and store it so that it can be used when there is a lack of it in their environment.1 Even if you were able to achieve a zero phosphorous level in the pool, these types of algae would still grow using the phosphorous stored within the cell. With these types of algae, removing phosphate does nothing to stop growth.
2. Phosphate removers do not hold a residual in the pool. So while some orthophosphate may be removed upon initial application, it will not be removed on a constant basis. And because phosphorous is so abundant, there will be a constant influx of phosphate. Phosphate will be introduced not only from the environment (remember – it’s the 11th most abundant mineral) but from bathers as well – it is a major component of proteins and will be present in skin, urine, sweat, etc. In fact, the tap water at the Technology Center has 1,500ppb (1.5ppm) phosphate and yet the test pools run successfully with no algae blooms on a regular basis.
3. And finally, the most important consideration is the presence of sanitizer or even better – sanitizer and algicide. Proper maintenance is the key to keeping algae growth in check. BioLab has conducted several studies to explore the phosphate issue. The studies used both lab cultured algae as well as algae obtained from the field. In these highly controlled, nutrient rich environments, algae did not grow in the presence of 1-2ppm chlorine. This was proven in multiple studies with varying phosphate levels up to 30,000ppb (30ppm). Furthermore, the use of a maintenance algicide enhanced water quality with increased clarity.
There has been much discussion regarding phosphates over the past several years. The fact is that phosphates are not “new” – they have always been present and are not more prevalent today than in the past. Keep in mind that consumers add phosphate based products for metal treatment on a routine basis. Some of these products include BioGuard® Pool Magnet Plus®, BioGuard Scale Inhibitor, GLB Super Sequa-Sol®, Jack’s Magic® The Purple Stuff™, Jack’s Magic The Blue Stuff™, Jack’s Magic The Pink Stuff™, ProTeam® Metal Magic, HTH® Stain and Scale, and Sparkle Conquest (this list is not meant to be comprehensive). Metal treatments with these products are performed with no chlorine demand or algae growth as a result.
Phosphates are and always will be a part of the environment. The best route to take is proper pool maintenance with products designed to kill and/or inhibit the growth of bacteria and algae.
1Griffith, Beeton, Spencer, Mitchell; Environmental Phosphorous Handbook, copyright 1973.
BioGuard Technical Information Bulletin
The information contained in this publication is based on data currently available to BioLab and is thought to be correct. Since BioLab has no control over the use of this information by others, BioLab does not guarantee the same results described herein will be obtained and makes no warranty of merchantability or fitness for a particular purpose or any expressed or implied warranty. This information is intended for use by technically trained personnel at their discretion.
