Phosphates, Nitrites & Nitrates in Swimming Pools – What do they do?
6th August 2009

Phosphates, Nitrites & Nitrates in Swimming Pools. What they are & what they do:

Phosphates & Nitrogen are 2 naturally occurring elements in nature. Phosphorous is a mineral & nitrogen is a gas. In nature, they don’t cause or contribute to swimming pool problems. However when they are “added” to the swimming pool water, problems can occur especially in a badly maintained swimming pool. The two most common problems are medium to large algae blooms and a massive chlorine demand. Both elements are essentially sat in the water waiting for algae to come along, eat them and then the algae will grow.

Phosphates typically come into the swimming pool from garden care products; fertilizers, sprays, etc. Phosphates can also come from dead skin cells. That’s why it is a good reason to shower before entering the swimming pool. These garden care products can be brought in from people walking on freshly treated areas where they are literally walked into the pool. They can also drift in when sprayed or just down to a windy day. Remember, phosphates can come from your garden, your neighbours garden or even from a local farmers field. Phosphates are often added directly into swimming pools in the form of “metal removers” and “stain control” chemicals.

Nitrogen can also come into your swimming pool from garden care products, but more typical, it’s in the form of sweat again shower before using the swimming pool, urine or other types of ammonia. If your local water supplier is using chlorine to sanitize the water, then large amounts of ammonia & therefore nitrogen are getting into the water. Algae loves both nitrogen AND phosphates.

Here’s the typical problem with Nitrogen. Nitrogen enters the water & combines with oxygen to form Nitrites. The nitrogen will typically take the oxygen from the chlorine that kills bacteria thereby causing a Chlorine Demand. You will have a difficult time maintaining chlorine, algae will thrive, the swimming pool water will become cloudy, etc. Once the nitrites have taken on more oxygen & become Nitrates, they are there to stay. The only way to remove Nitrates from the water is to drain & refill with fresh water that is hopefully not contaminated with Nitrites. Shocking & oxidizing the swimming pool will help to a certain degree. Nitrates you can live with, Nitrites are the problem causers.

With either Phosphates, Nitrites or Nitrates present, as long as a good, solid chlorine or bromine level is maintained, there normally isn’t a problem with your swimming pool. However, when the chlorine is stressed out due to high bather loads, parties, rainstorms, etc. or if there is an existing chlorine demand problem, phosphates & nitrates just feed right into any algae present & the problem worsens significantly.

A really simple way to ensure you minimise your algae issue is to use a Flocculent. These simply remove phosphates from the water by binding them together to allow them to be filtered and then washed away when the filter is cleaned.

In performing a side by side test to prove the significance of phosphates in swimming pool water, in swimming pools treated the same there was no difference in water quality and clarity between the control swimming pool and the swimming pool that regular additions of phosphate made to the swimming pool water.

The simple solution follow the 4 steps of good swimming pool water chemistry:

1. Maintain a constant level of sanitizer (chlorine, bromine, etc.);

2. Shock the pool regularly to oxidize environmental waste;

3. Add algaecide regularly to prevent algae growth;

4. Maintain proper levels of pH, total alkalinity, calcium hardness.

By following these simple steps you should never have a green pool.

