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Phosphates – A Growing Problem For Pools



ore and more I am dealing with pools that are experiencing problems with higher than previous chlorine demands

and outbreaks of algae. Why? Because phosphates are now being added by the water companies to the water supply and these are basically fertilisers that encourage the growth of algae.

WHY ARE WATER COMPANIES ADDING PHOSPHATES? To comply with EC directive 80/778/EEC that demands that drinking water contain less than 10ug/l of lead by December of this year. To understand this there are a 1,000 ug/l in a mg/L or ppm in old money.

The cost to replace all lead piping (which is the responsibility of the water companies) has been estimated at up to £10bn. When you consider that the majority of these companies already lose 25% of their treated water through leaks, you would imagine that would be incentive enough, but sadly not.

Instead of replacing these pipes, the water utility companies will add phosphates to the water supply to inhibit corrosion. The forms of phosphates used create orthophosphate, which forms a protective coating of scale on the inside of service pipe work and household plumbing. This hopefully prevents the corrosive elements in water from dissolving some of the metal in the drinking water. To prevent plumbo- solvency (lead poisoning) through chemical treatment, the Drinking Water Inspectorate (DWI) recommends orthophosphate should be maintained as a residual in supply at 0.5-1.0 mgP/l, with the pH between 7.2 – 7.8 and this is likely to cause problems to those in the pool industry.

WHAT ARE PHOSPHATES? Phosphates are a natural mineral that is mined and used in many of today’s off the shelf products, including, washing powders (or liquids) personal hygiene products (deodorant, shampoo, etc), and even some food products. The addition of phosphates to dishwashers helps to soften the water and prevent soiling being deposited on plates, etc. The problem with this addition is it finishes up in natural water, lakes, ponds, streams and rivers where it encourages excessive algae growth.

68 December 2013 SPN


Phosphates provide nutrients for algae. The higher the level of phosphates in a pool, the more microscopic algae that you’ll also have in the pool. Since more of your free chlorine is then occupied killing algae, less is available to form a disinfectant residual. High phosphate loads, when left untreated, will generally result in higher chlorine demand and can even lead to algae ‘blooms’ in your pool. A higher chlorine demand can overwhelm your chosen chlorine supply. For operators using granular or liquid chlorine, for example, high phosphate levels can result in unnecessarily high chlorine bills, due to using more chlorine than otherwise would be necessary to kill the algae in the water. Phosphates can by their nature, also contribute to the forming of scale which causes problems on your pool and plant equipment. If possible, maintaining a zero phosphate residual reduces your pool’s chlorine demand, making savings on chemical costs and the chlorine dosing equipment.

HOW CAN YOU TELL IF YOU HAVE A PHOSPHATE ISSUE? Test your pool water and the source of supply regularly with a good test kit or alternatively send it to me (in a container obviously). There are digital test kits available that are very accurate and are very simple to use. There are also older styles of ‘colour comparator’ test that will usually measure up to 1,000ppb. The accuracy of these tests is not as good as a digital meter and they are not as useful if your phosphate level is greater than 1,000ppb, but they can be used as a starting point in diagnosing a phosphate problem. Be careful though as if there is already an algae bloom, you may get a low or zero reading as the phosphates have already been consumed. It is not until the algae die

that the phosphates are released into the water again and can be detected.


Phosphates will not disappear on their own. They must be removed with a chemical specifically designed to do the job. I recommend a high strength phosphate remover. Options for phosphate removers have exploded over the past few years, due in part to the popularity of salt systems, which means that you have many options. Selecting the correct one for your application will be based on your ambient phosphate level and ongoing phosphate reduction needs. Beware, though, because many are not worth the price.


First, regardless of the system you use, chlorine usage goes up. If you have always had high phosphate levels, you have likely always been using more chlorine than otherwise would be necessary to create a safe residual. Second, your combined chlorine readings will generally increase. This is due to the chlorine attacking the algae that is forming in your pool, which reduces the free available chlorine and increases the combined chlorine levels. Those with a properly sized UV system may not see this, as the UV destroys the chloramines as they are formed. Third, you may see algae blooms. If your chlorine drops down low overnight or during the day and is not brought back up quickly, you’ll see algae start to take over. This of course means you’ll need to treat with an algaecide and/or shock the pool to deal with the algae. Finally, you may find that you are getting scale build-up that is not easily removed. Should this happen, you are likely in for some work getting your pool back in line, removing the scale and finding an appropriate way to prevent more from forming. My best advice when it comes to phosphates is to not ignore them and not to let them get out of hand. Treat them aggressively and remove them. It is far easier to balance your pool and keep it clean and clear when you do not have a phosphate load.

Studies In Work 01452 417533

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