What are Phosphates?
Phosphates are a type of ion with the formula (PO4). When a phosphate containing compound is added to water, it will form Phosphoric Acid.
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 even used in some foods. It’s ability to sequester metals while being low toxic has led it to be a widely used compound in swimming pool chemicals.
At the dawning of Tide Laundry Detergent and various dish soap in the first half of the 20th century, phosphates were a key ingredient. Phosphate would chelate calcium from water improving their efficacy.
Organic or organophosphates are a specific type of carbon and phosphate containing compounds. Unlike other forms of phosphates used as sequestrients, organophosphates act as a nerve agent and are widely used as an insecticide. However they are becoming increasingly regulated due to potential health risks.
Why do Phosphates Matter?
Phosphate is considered a limiting nutrient for algae in freshwater. This means in theory algae will grow up to a certain point depending on the amount of phosphate available. This is particularly relevant for the ecology of freshwater environments.
When phosphates were used in detergents and soaps, wastewater would enter rivers, ponds, and lakes. This would increase phosphate levels and lead to a dramatic rise in algae (referred to as Eutrophication or nutrient pollution). The larger algae blooms would lead to oxygen depletion, causing the death of other organisms in the ecosystem – such as fish and insects.
This led to the banning of 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.
According to Water Research Center, 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): 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
Phosphates are also a concern for man-made fish habitats – a.k.a Fish Tanks. 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 I need to worry about Phosphate in my pool?
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 is less important in you pool:
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 an algae control themselves – by 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 phosphate control 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 levels 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 phosphate levels 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 – although informal – 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.
The samples were then left in sunlight and allowed both samples to grow algae by leaving it in the sun. Everytime they performed the experiment the results were the same; there was no discernable difference in the amount of algae grown between the two samples.
It’s interesting to contrast this with the Water Research 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, water temperature was found to be a primary driver of algae growth. This supports McGrayel’s study where the water samples were left in sunlight.
Then why are there Phosphate Removers?
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. However, 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 their efficacy (where 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. And at a much lower cost.