Phosphates… What are they and why should you care?

In Blog, Chemistry by Aaron Donohue

What are phosphates?

Phosphates are a natural mineral that is mined and used in many of today’s off the shelf products, including some pool treatment chemicals, personal hygiene products (deodorant, shampoo, etc), and even some food products.

How do phosphates affect pool care?

Phosphates are food 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 sanitizer 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 tax, or even overwhelm, the production capacity of a chlorine generator. 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.

As referenced in another blog (Scaling not just calcium), phosphates can also contribute to some very troublesome scale that can wreak havoc on your pool and equipment.

Maintaining a low (or zero) phosphate residual reduces the overall chlorine demand, saving money on chemical costs and reducing the work load on all chlorination equipment. This can lead to longer equipment lifespan, especially when working with a chlorine generator.

How can you tell if you have a phosphate issue?

Simple: Get a good test kit. There are a few digital test kits available that are very accurate and are very simple to use.  There are also older styles of “color comparator” test that will usually measure up to 1000ppb. 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 1000ppb, but they can be used as a starting point in diagnosing a phosphate problem.

How can you remove the phosphates?

Phosphates do not disappear on their own. They must be removed with a chemical specifically designed to do the job. We 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. For our own clients, we’ve spent over a decade testing different brands of remover and test kits, just to find the best product for the job. We’ve even gone as far as automating the feed of phosphate remover for clients who have particularly high or troublesome phosphate issues. Your best bet is to contact your tech support rep for help with selecting the correct one.

What happens if you don’t do anything about the phosphates?

First, chlorine usage goes up.  Whether you are using granular, liquid, an Electrolytic Chlorine Generator, or some other form, usage will increase. 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 buildup 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 present.  It is far easier to balance your pool and keep it clean and clear when you do not have a phosphate load.