There is a debate in the industry whether phosphates in pools really matter. One side says using phosphate removers are an integral part of maintaining an algae free pool, while the other says it’s a total waste of money. In this article, we break down the science to give you an answer.

What are Phosphates?

phosphate ionPhosphates are a type of ion with the formula (PO4). When a phosphate containing compound is added to water, it will form Phosphoric Acid[1].

Phosphates serve several functions in water. Phosphates act as a detergent, as a buffering compound, and as a sequestering agent for metals in water. It also has low toxicity – and is even used in some foods.  It’s ability to sequester metals while being low toxic has led it to be a widely used in swimming pool chemicals.

Phosphates were a key ingredient for Tide Laundry Detergent and various dish soap in the first half of the 20th century,  Phosphate would chelate calcium from water improving their efficacy.

Organic or organophosphates are specific types of carbon and phosphate containing compounds. Unlike forms of phosphates used as sequestrants, organophosphates act as a nerve agent and are widely used as an insecticide. However, they are becoming increasingly regulated due to potential health risks[2].

Why do Phosphate Levels matter?

Phosphate is considered a limiting nutrient for algae in freshwater. This means in theory algae will grow depending on the amount of phosphate available. This is particularly relevant for the ecology of freshwater environments.

Eutrophication

1. Excess nutrients are applied to the soil. 2. Some nutrients leach into the soil where they can remain for years. Eventually, they get drained into the water body. 3. Some nutrients run off over the ground into the body of water. 4. The excess nutrients cause an algal bloom. 5. The algal bloom blocks the light of the sun from reaching the bottom of the water body. 6. The plants beneath the algal bloom die because they cannot get sunlight to photosynthesize. 7. Eventually, the algal bloom dies and sinks to the bottom of the lake. Bacteria begins to decompose the remains, using up oxygen for respiration. 8. The decomposition causes the water to become depleted of oxygen. Larger life forms, such as fish, suffocate to death. This body of water can no longer support life. From Wikipedia.org

Phosphates used in detergents and soaps, enter rivers, ponds, and lakes through wastewater. This increased phosphate levels in lakes and ponds and lead to a dramatic rise in algae (referred to as Eutrophication or nutrient pollution). The larger algae blooms led to oxygen depletion, causing the death of other organisms in the ecosystem – such as fish, plants and insects.

This led to the banning of the use of phosphates in laundry detergent and dish soaps. Currently available detergents and soaps in the U.S. and Europe do not use phosphates since these products directly contribute to wastewater[2].

According to Water Research Center[3], a consulting firm in the ecological space, the following are approximate guidelines for phosphates related to algae growth:

  • 0.01 – 0.03 mg/L (10 – 30 PPB): the level in uncontaminated lakes
  • 0.025 – 0.1 mg/L (25-100 PPB): the level at which plant growth is stimulated
  • 0.1 mg/L (100 PPB): maximum acceptable to avoid accelerated eutrophication
  • > 0.1 mg/L ( > 100 PPB): accelerated growth and consequent problems

Fish Tanks

Phosphates are also a concern for man-made fish habitats like fish tanks and aquariums. Since too much algae can deplete oxygen and ruin the aesthetics, fish tanks require some level of algae control. However, fish are sensitive to most forms of sanitizer, making the use of chlorine impractical. One option is to limit and/or remove phosphates from the water. Fish then feed on any remaining algae to bring the system into balance.

So do we need to worry about Phosphates in Pools?

Simply, no. While phosphates do play an important role in larger ecosystems, pools for recreational swimming are quite different. Here are a few reasons why the role of phosphates in pools is less important:

Pools need Sanitizer

Unlike freshwater ecosystems – like your nearby lake or fish tank in your home – pools utilize sanitizer such as chlorine. Since pools don’t typically have fish, there is no limitation on utilizing sanitizer. Also, fish act as a form of algae control themselves – feeding on algae growth.

Swimmers naturally swallow some water while swimming. Sanitizer is necessary to prevent the growth of harmful algae and bacteria that can lead to illness, thus rendering phosphates in pools irrelevant. Even in a pool where there is zero phosphate (something impractical to maintain), sanitizer is still required.

Phosphates prevent Stains and Scale

Stains are also a unique concern in pools.

Phosphates are a strong metal chelator – thus removing and preventing stains and scale. Removing all phosphates would likely lead to an increase in staining frequency, while greatly reducing the types of stain removers that can be used. Thus, high phosphate in pools are beneficial to stain prevention.

Phosphate Removers are not cost Effective

Phosphates are constantly being introduced into a pool via stain removers and runoff. This makes maintaining near-zero phosphates in pools impractical. When compared to the efficacy of proper sanitation and algaecide, phosphates removers offer little benefit relative to their cost.

McGrayel Study of Phosphates

In an interesting study by McGrayel (the manufacturers of the Easy Balance line of products), they compared a distilled water sample without phosphates with a tap water sample containing 1000 ppb of phosphates[4].

The samples were left in sunlight and allowed to grow algae. They then measured the amount of algae growth. Every time they performed the experiment the results were the same; there was no discernable difference in the number of algae grown between the two samples.

It’s interesting to contrast this with Water Research’s Guidelines, where 1000 PPB is 10x over the accelerated growth limit. We could assume that this is due to the fact that in the McGrayel study, competing species – such as plants and fish –  are not considered.

In a University of Wisconsin study of Black Algae in lakes[5], water temperature was found to be a primary driver of algae growth. This supports the findings McGrayel’s study where the water samples were left in sunlight.

Why are there Pool Phosphate Removers then?

Two words: clever marketing. Manufacturers of phosphate removing chemicals for fish tanks were looking for additional markets to sell their products. And there are more pools than there are fish tanks. For example, Natural Chemistry began in the Pet Care industry and is likely the market leader in the Phosphate Removal segment.

Phosphate Remover manufacturers began marketing efforts centered around promises of cutting down on algaecide and chlorine costs. Customers were intrigued by the “one thing missing” in their battle against algae. Retailers jumped on board the idea as an opportunity to sell an additional product to their customers.

Some customers do swear by phosphate removal. It’s unclear whether it is simply confirmation bias, or whether they provide some relief in extreme cases. Yet, while there is a fair amount of adoption by retailers (who have an interest in selling additional products to consumers), there is wider debate amongst service professionals about phosphates in pools (where the cost of service is a consideration).

While phosphates are indeed a concern in terms of environmental impact, they are much less of a concern in swimming pools. Maintaining proper sanitizer, and utilizing a decent preventative algaecide, will prevent algae regardless of phosphate levels at a much lower cost. In addition, you can utilize phosphates for their benefits.

What do you think? Do phosphates in pools matter? Leave us a comment!

References

  1. https://en.wikipedia.org/wiki/Organophosphate
  2. https://en.wikipedia.org/wiki/Phosphates_in_detergent
  3. https://www.water-research.net/index.php/phosphates
  4. http://gochemless.com/pdf/Phosphate_Facts_and_Myths.pdf?width=1400&height=900&iframe=true
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC243093/pdf/aem00213-0042.pdf

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