Phosphate removers and algaecides: a how-to guide


By Paul Simons, Managing Director
Monday, 17 October, 2016

Phosphate removers and algaecides: a how-to guide

What’s the deal with phosphate removers and algaecides? How do they work and how should you use them? Paul Simons, Managing Director of Lo-Chlor Chemicals, explains.

The 4th of November 1994 was a very important date in the Australian pool and spa industry. That year, a gentleman by the name of Dudley John Mills walked into the offices of Lo-Chlor Chemicals, sat down with the company’s management and presented them with a white milky substance. He claimed that this invention would revolutionise the way we treat water — in particular, how we maintain an algae-free environment in swimming pools (both domestic and commercial).

Several months later and after extensive testing in the laboratory, Lo-Chlor Chemicals realised Mills’ claims had real substance, and the first phosphate remover globally — simply known as Starver — was born.

Twenty-two years later, Starver is the single, highest-selling specialty chemical in the Australian pool industry and almost every chemical company across the globe has some form of phosphate remover in its range to combat long-term algae problems and stubborn algae strains.

Phosphates and nitrogen: the basics

Phosphates and nitrogen are two naturally occurring elements in nature.

Phosphorous is a mineral, while nitrogen is a gas. In nature, they don’t cause or contribute to pool problems. However, when they are added to the pool water, problems can arise — especially in a poorly maintained pool.

The two most significant problems are moderate to severe algae blooms and chlorine demand. Both elements essentially create a buffet table for any algae to arrive, eat and thrive.


Phosphates typically enter the pool from lawn care products: fertilisers, sprays, etc. Phosphates can also come from dead skin cells, body fats and oils. (Yet another good reason to shower before entering the pool.)

Lawn care products can be brought in from people walking on freshly treated areas; they are literally walked into the pool. They can also ‘drift’ in when sprayed nearby or can be carried quite some distance into the pool on a windy day. Remember, phosphates can come from your yard, your neighbour’s yard or even from someone you don’t know who lives three blocks away.

Phosphates (or forms of phosphorus) are often added directly into pools (yes, really!) in the form of ‘metal removers’ and ‘stain control’ chemicals. Most pool sequestering or chelating products contain phosphorus.


Nitrogen can also come into your pool from lawn care products, but more typically, it’s introduced through sweat (when swimmers don’t shower before using the pool), urine (when swimmers don’t use the facilities before going into the pool) or other types of ammonia. (Ammonia is composed of nitrogen and hydrogen — NH4.)

Here’s the typical scenario: nitrogen enters the water and combines with oxygen to form nitrites (NO2). The nitrogen will typically take the oxygen from the HOCl (hypochlorous acid — the form of chlorine that kills bacteria and algae), thereby causing a chlorine demand. You will have a difficult time maintaining chlorine, algae will thrive, the water will become cloudy, etc. Once the nitrites have taken on more oxygen and become nitrates (NO3), they are there to stay.

The only way to remove nitrates from the water is to drain and refill with fresh water that is hopefully not contaminated with nitrites. It’s been proven that using no-chlorine shock treatments and oxidising compounds will help to a certain degree. Nitrates (NO3) you can live with; nitrites (NO or NO2) are the problem causers.


Phosphates are a vital plant nutrient and their presence in swimming pool water, even at low concentrations, can cause accelerated algae growth in poorly maintained pools.

Pools that are properly maintained and kept in balance usually do not have unexpected difficulty controlling algae, but the presence of phosphates can make algae control more difficult to control, and you’ll need to increase the amount of sanitiser to maintain satisfactory control of algae.

Fortunately, when it comes to phosphates, there are options available to remove this contaminant from the water.

Back in the good old days, algae strains were treated like any other pool problem: chuck in some acid and chlorine and “she’ll be right mate”. What we ended up with was very acidic pools which in turn destroyed concrete surfaces and equipment over time.

These days, we are far more educated and there are a number of treatments available to remove algae and maintain an algae-free environment.

The biggest advantage of using algaecides and phosphate removers rather than chlorine and acid is that the former are far safer to handle and much easier to use than the latter, and they deliver guaranteed results if used correctly and purchased from a reliable source.

Phosphate removers versus algaecides

Phosphate removers are not algaecides. They will not clear up green/pea soup pools and they do not kill algae. One mistake a lot of people make is that they see a green pool or black spot algae and they start their treatment with a phosphate remover. This is not the correct way to manage the problem and is a waste of money.

You see, algae thrive on the phosphates as their food source, so if there are algae present in the pool, you can be certain the phosphate level is low or even zero. This is because the algae have actually consumed the phosphates as they are using them as a nutrient to survive. When we kill these algae strains they release a portion of those consumed phosphates back into the pool water. This is a key process in understanding long-term algae prevention.

So how do we treat algae strains correctly and how do we ensure the long-term prevention of these strains?

Firstly, you must kill off the algae. There are more than 2 million strains of algae in the atmosphere so it’s important you understand the type of algae you are dealing with and the best product to use to kill that algae. Fortunately, we only see a handful of these and usually place them in two separate categories to make it simple. Clinging algae such as black spot and mustard algae are one type; floating algae such as green and red algae are the other. (Very rarely, we see purple and pink algae, but they do appear at certain times of the year.)

Clinging algae

In porous pools such as pebble, concrete, exposed aggregate and tiled pools (the grout being the porous surface), the common algae we see is the clinging algae, which actually grows down deep into the porous surface. Algae is a plant matter and, like all plants, has a root system. These roots penetrate deep into the surface and if you use cheap algaecides or just straight chlorine you will only kill the tip of the algae and it will return within weeks, if not days.

Look for an algaecide that has a combination of copper and a quaternary ammonium compound (an example of such an algaecide is Tropiclear Pool Algaecide). Copper is an excellent algaecide and has been scientifically proven to provide long-term algae prevention. Quaternary ammonium compounds are also known as wetting agents and they are excellent at penetrating deep into the root system of the algae once that top layer has been taken off. Quaternary ammonium compounds are also excellent for these algae strains but they do not have longevity of copper so a combination is preferred.

Floating algae

Green or floating algae are far easier to treat but like all algae strains they will regenerate and grow back quickly if not treated correctly.

As with the black spot and mustard algae, using straight chlorine or cheap algaecides will give you superficial results. The algae will return in a short amount of time and you will have dissatisfied customers.

Choose an algaecide that is right for the situation. Copper compounds are very good for a vast array of algae types and will give you long-term algae prevention after the algae has been killed (up to 90 days). Some algae do build up a resistance to copper so as an alternative you can look for compounds known as polyquats (polyquaterniums) or oxiranes (such as Miraclear Pool Algaecide). These are non-copper alternatives that provide a fantastic result when treating green algae in particular. They are non-dangerous and very easy to handle, so there is no need to use heavy concentrations of chlorine when treating algae.


Once the algae have been removed (killed), they release the phosphates back into the water. This is the ideal time to hit them hard with a bulk phosphate remover that removes high levels of phosphates (like Starver X by Lo-Chlor) at the start of the process. Then get your customer onto a phosphate-removal maintenance program.

They key to finding the right phosphate remover is looking for one that will efficiently remove extremely low levels of phosphates. Phosphate levels above a mere 0.2 ppm (parts per million) will create an environment where algae can grow. There are only a few on the market that can achieve this level and maintain it all year round so choose wisely. Not only will this provide your customer with an algae-free pool for the entire year, but they will find over time there will be less need to use high concentrations of sanitiser and they will have far fewer problems in the long term.

A simple message to remember as we head into what is shaping up to be the hottest summer on record: no phosphates means no algae.

For more information on phosphates and their removal, visit the troubleshooting section of the Lo-Chlor website:

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