Iron in Aquaculture Ponds

Iron in Aquaculture Ponds
Iron in Aquaculture Ponds

Iron is a major problem in Southeast Asia for aquaculture ponds in coastal areas. In Asia some 7 million hectares (Mha) are acid sulphate soils, heavy in iron.



The high iron concentrations come from either pyrites or accumulated iron in mangrove swamps. When the ground is disturbed with pond excavation, oxygen is introduced. This produces iron complexes and sulphuric acid (H2SO4).

Pyrites compete with aquatic life for more oxygen to oxidise and become ferric ion (Fe3+).

Water and pond bottom becomes acidic, and iron is observed in the pond.

While some level of soluble iron is desirable in aquaculture ponds, medium to high levels cause problems:

Beneficial algae growth is inhibited.

pH is often acidic, which can cause stress in both fish and prawns.

High iron levels can react with organics in the pond producing a colloidal iron complex, which reduces oxygen transfer and can cause suffocation of living organisms.

High iron in water can cause stress on fish and prawns, which often results in a reduction in growth and in some cases the appearance of Early Mortality Syndrome (EMS) throughout the pond.

Vibrio bacteria usually favours acidic conditions and feeds on soluble iron, which can prevent the viability of the whole pond.

Farmers often complain of loss of crop after heavy rain events. When the sludge is not disturbed and no additional oxygen (other than that provided by paddle wheels) is introduced, the pond usually remains relatively healthy with beneficial algae being the dominant species. But if the vibrio load is high in the pond, the chances of getting EMS will greatly increase. Heavy rains can disturb acid sulphate soils, as pyrite releases hydrogen sulphide (H2S) and iron (Fe2+). This soluble Fe2+ increases oxygen demand to produce insoluble Fe3+, while H2S is toxic to shrimp. This explains why heavy rains can cause stress in aquaculture ponds.

Source: P. Byrne, P. J. Wood & I. Reid (2012): The Impairment of River Systems by MetalMine Contamination: A Review Including Remediation Options, Critical Reviews in EnvironmentalScience and Technology, 42:19, 2017-2077


Why AQUA-Cal+ is an ideal solution for the flocculation and removal of iron (and other heavy metals)

  • The hydroxyl ions (OH-) in the magnesium hydroxide Mg(OH)2 slurry react with the metal ions to form insoluble metal hydroxides.


AQUA-Cal+ can flocculate iron

AQUA-Cal+ can flocculate iron

2 Days after treatment


Cost comparison of AQUA-Cal+ with traditional treatments for iron

* The cost of traditional treatments was provided by one of our Vietnamese customers. Costs may vary by region and situation.

Source: Hoffman Environmental Inc., 2002, Wastewater Treatment System, Texas, USA.


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Iron in Aquaculture Ponds


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