Frequently Asked Questions (FAQs) & Answers

Short answers to some common questions can be found here. A more detailed answer to each question can be viewed by clicking "read more" at the end of the answer.

The questions:

About the product itself

Use and Application

Background & additional information

Questions & Answers:

About the product itself

What is Phoslock?

Granular-2-4_bis.jpgPhoslock is a modified clay product which removes soluble phosphorus from all kinds of water bodies including fresh, brackish and saline water. Removal of phosphorus reduces 'eutrophication' as indicated by the presence of algal blooms in water.
Read more

What is Phoslock made from?

Phoslock is made from naturally occurring products. The manufacturing process involves combining a naturally occurring clay (bentonite) with a rare earth (lanthanum). Lanthanum is absorbed into sites within the bentonite and becomes the active element to remove phosphorus.

How does Phoslock work?

When Phoslock is applied to a water body, the phosphorus present in the water column is attracted to the lanthanum to produce lanthanum phosphate. Lanthanum phosphate is very insoluble and therefore phosphorus remains locked up within the bentonite.
After a couple of hours, the Phoslock will settle on the sediment and so long as it has active sites it will continue to react with any phosphorus either released from the sediment or present in the water.

How was Phoslock developed?

Phoslock was developed in Australia by scientists at the Federal research organization, the CSIRO, and funded jointly by the Western Australian State Government's Water and Rivers Commission and the Swan River Trust. The research was initiated in late 1994 to remediate the Swan and Canning Rivers by reducing the level of phosphorus.
Read more

Is Phoslock environmentally safe?

finlDSC04740-266.jpgYes. Phoslock has been the subject of extensive ecotoxicity and other testing in a number of countries including Australia, USA, China, Germany, the Netherlands and New Zealand. The most comprehensive tests were conducted in NZ on algae, juvenile fish (rainbow trout) and water fleas (crustacea). These are known to be very sensitive indicators of contamination or pollution. These tests demonstrated that, under NZ ERMA guidelines, the risk posed to these organisms is so very low that Phoslock is regarded as 'non-toxic'.
Read more

Use and Application

How is Phoslock applied?

Phoslock is applied using shore or boat based equipment.
Shore based application involves slurrying the dry granules on site using site water and spraying the slurry onto the water using a pressure hose. Boat based application also involves slurrying, using on-board equipment and broadcasting by hose and a spray boom.
The water will be milky for a few hours after application before returning to its previous state, the only exception being that the phosphorus will be reduced and will fall to below measurable amounts with the right level of application.
Read more

What is the best time to apply?

In order to remove as much phosphorus as possible, the best time to apply Phoslock is when most phosphorus in the water column and sediment pore water is in a form which can be removed by Phoslock (i.e. ortho-phosphate or FRP). Once phosphorus is taken up by the biomass (e.g. during an algal bloom), it is converted to organic phosphorus and is not in a form that will readily bind with Phoslock. The period in which most phosphorus is in the FRP form varies from lake to lake. For the temperate and continental climates (most of Europe), this occurs in general over the autumn and winter periods, during which time algae die off and organic phosphorus is released and subsequently mineralised to FRP. Therefore the best time to apply in these climates is from early autumn to early spring.

How often does Phoslock need to be applied?

Treatment with Phoslock provides a "reset" of the ecological clock of the water body. That is, it returns the water body to the phosphorus level which is likely to have existed many years prior to the events which have given rise to the increased levels.
Management strategies limit additional nutrients finding their way into the water body. However, it is rarely possible to prevent nutrients building up as there are various sources of new nutrients including runoff and waste from birds and animals. Phoslock may remain active and capture phosphorus from natural sources for many years.
However, if there are unmanaged phosphorus inputs, Phoslock treatment may be required at much more regular intervals.

Where is Phoslock being used and in what applications?

finlDSC04748-266.jpgPhoslock has been used in over 20 countries.  These include Australia, New Zealand, the U.S., Canada, Germany, Netherlands, U.K., Poland, Singapore, Malaysia, Indonesia, Korea, Brazil and South Africa.

Types of water bodies treated include large lakes, drinking water reservoirs, irrigation channels, rural and semi-rural water bodies, golf course ponds, ornamental lakes in universities and office parks, prawn farms and artificial wetlands.

Read more


What regulatory approvals have been obtained?

Detailed information about the approvals that have been received relating to Phoslock use in different parts of the world is available on our Approval page. 

Read more

Background & additional information

What is FRP?

SA-Feb-02-071-266.jpgFRP stands for Filterable Reactive Phosphorus

What is Eutrophication?

Eutrophication means nutrient rich - usually referring to the presence of excess phosphorus and nitrogen. Phosphorus is easier and more cost effective to control to make water bodies clean.
Apart from algal blooms, eutrophication can lead to fish kills with loss of other aquatic life, it can kill animals that drink the water and some types of algae can make humans very sick.
Read more

What are the options for dealing with algal blooms?

SA-Feb-02-060-266.jpgThere are a number of strategies to deal with algae.  These include draining the water body and dredging the sediment, applying an algicide and treating the water with chemicals such as aluminium and iron salts or Phoslock.

Sediment dredging can be an effective measure to remove phosphorus from water and sediments, however it is messy, disputive to benthic life and generally very expensive.

Algicides are a short term measure as the phosphorus returns to the water when the algae die, providing a food source for more algal growth.  Care is also required when using algicides as dangerous toxins may also be released into the water as the algae die.  Most algicides are copper based and are not environmentally friendly.  In many parts of the world, many of the commercially available algicides have been prohibited from use.

Water treatment chemicals such as aluminium and iron salts are also commonly used to control algae.  These methods may be inexpensive, but the phosphorus that is removed can be re-cycled by bacteria, meaning that re-treatment is then required.  Aluminium and iron phosphate tends to be either pH or redox sensitive, with the result that phosphate bound from an application of aluminium or iron salts may potentially be re-released when environmental conditions change.  Furthermore, very large dosages are frequently required in order to achieve the very low levels of phosphorus that are required for good water quality.  These dosages can make water acidic and kill sensitive species.

Phoslock, on the other hand, reduces phosphorus to very low levels, without any of the disadvantages associated with the methods described above.

What is Lanthanum?

Lanthanum is a chemical element with the symbol La and atomic number 57 belonging to group 3 of the periodic table and is one of the lanthanoids. In its pure form it is a silvery white metallic element.
Read more

What is Bentonite?

Bentonite is a natural clay consisting of smectite minerals. There are a few types of bentonites and their names depend on the dominant elements, such as K, Na and Ca.
Read more