A new tool for pond managers.
Pond managers can now fine-tune the performance of their ponds by controlling the level of phosphate in the water. Phoslock is a pond management tool that has never before been available to managers who can now have a much higher degree of control over their ponds than they have had in the past. See here for the details of why Phoslock is unique.
Excess phosphate in ponds is problematic for a number of reasons:
excessive PO4 can lead to development of excessively dense algal blooms: by controlling the level of PO4 managers can maintain blooms at the levels they desire for their particular type of farming operation.
excessive PO4 can lead to large diurnal pH fluctuations: these fluctuations can stress fish and shrimp, and lead to dangerously dense algal monocultures.
excessive PO4 can increase risk of development of potentially dangerous algal blooms: control of PO4 allows managers to easily set the required N:P ratio they desire to avoid or manage toxic algal blooms. See the experience we had on our farm by clicking here.
excessive PO4 can produce cyanobacterial (blue green algae) blooms: such blooms develop when PO4 is high relative to N. Managers now have the ability to control and manage these blooms by bringing the PO4 back to optimum levels. Click here for more information.
excessive PO4 can lead to off-flavor: cyanobacteria are favored by a low N:P ratio and this can lead to growth of blooms that produce off-flavors in fish and shrimp.
excessive PO4 can reduce plankton diversity in aquaculture ponds: plankton diversity leads to stable, productive and low risk ponds. Ponds with high PO4 tend to have dense monocultures which are inherently unstable and risky. These monocultures are a result of biological, chemical and physical factors such as for example: high diurnal pH fluctuation, autoshading, the high level of PO4 itself which favors some algae (eg cyanobacteria, some brown flagellates and some dinoflagellates) over others. Managers can now control PO4 to achieve diverse and stable blooms
excess PO4 can produce dangerously low dissolved oxygen in the pond: this happens because the algae bloom can become too dense leading to low night time oxygen levels and increased risk of plankton “crash”
excessive PO4 pollutes surrounding aquatic/estuarine/marine environment. The only option managers have had in the past is to exchange water and drain the excess PO4 into the surrounding environment. Managers can now minimise the amount of PO4 from their farms and help maintain or even improve the water quality of their immediate aquatic surrounds.
At what level is PO4 excessive? In aquaculture ponds it is desirable to have adequate PO4 to allow the development of a healthy and diverse bloom of algae and bacteria in the pond. As a general rule, once the desired water quality parameters are achieved then any measured PO4 can be considered to be in excess and it is desirable to limit this to less than 0.03 mg per litre. See here for more details. For example, a shrimp farmer would measure the PO4 when his pond is in the condition he desires, then take steps to reduce the PO4 down to less than 0.1 mg /L. Traditionally, his principle means of doing this is to change water. With Phoslock he has the additional tool available to him to apply the product and so bind up the excess PO4 so that he can reduce the need to exchange water. The benefits of reducing the necessity to change water can be far reaching for the farmer, as it can substantially reduce his costs of pumping and can also have a very real effect in reducing the risk of introducing polluted water or disease to his crop. See here for more details.
How can we measure PO4? Simple and inexpensive test kits provide a means to measure PO4. On our farm we use a PalinTest photometer. We filter the water through a 1 um filter before testing. The whole procedure is done in 10 minutes.
What are the sources of PO4? PO4 comes from the initial fertiliser used to stimulate the bloom, from water pumped into the pond, from the pond soil, and most importantly, from the feed. Less than 15% of the PO4 in the feed is incorporated into the shrimp or fish, the other 85% goes back into the water. As a general guide each tonne of feed can add as much as 30 kg PO4 to the pond.
How can we control PO4? Judicious use of fertilisers is important to ensure that PO4 is not too high. Pond managers know what is best for their farms when it comes to fertilisation. However, Phoslock is a NEW tool and some alterations to previous practice will occur as managers grow accustomed to the advantages that Phoslock can bring to the way they manage their ponds. Water exchange has been the traditional way to manage blooms. Phoslock will come to be seen as an additional and alternative management tool to water exchange.
How much Phoslock is required? This is impossible to answer simply because all ponds are different. The amount of PO4 in the water depends on the soil type, the fertiliser history, the water source, history of water exchange, the age of the pond, feed quantity and the type of feed being used. Each pond manager will assess the requirements for his ponds. As a general guide, the measurable PO4 should be kept at less than 0.1 mg per L when the pond bloom is in the stage that is preferred by the farm manager.
How do I calculate the Phoslock requirement for my pond? This is a simple 3 step calculation:
Step 1: measure the amount of PO4 in the pond water
Step 2: calculate the total amount of PO4 you want to remove
Step 3: calculate the total amount of Phoslock you need to add.
Here is an example: your pond is 2000 cu m, the PO4 is 0.5mg per L, and the bloom is just right for your situation. So you need to remove 0.4 mg per L to bring the PO4 down to 0.1 mg per L. The total amount of PO4 you need to remove is 0.8 kg PO4. To remove this you need to add 0.8 x 30 kg Phoslock or a total of 24 kg. That is, for each kg of PO4 you need to remove, you need to add 30 kg of Phoslock. It's that simple.
How safe is Phoslock? Phoslock was developed in Australia by the CSIRO, the premier R& D organisation in Australia. The product was developed as a safe and natural way to control algae in water bodies and works by binding permanently with PO4 making the PO4 unavailable for algal growth. Phoslock is safe for humans and for all aquatic life. Phoslock is NOT an algicide. It controls algae not by any toxic effect, but by removing the primary nutrient PO4.
For an interesting overview of P in natural waters, go here