What Causes Algae Die-off in Ponds? Detailed Explanation of Causes and Prevention Methods

Friends in aquaculture all know that once algae die-off occurs in a culture pond, the fish and shrimp in the water are in danger. If it cannot be handled properly in time, it can easily cause rapid deterioration of water quality and mass death of fish and shrimp, causing great economic losses to farmers! What is pond algae die-off? How to prevent and control the occurrence of this phenomenon?

1. What is pond algae die-off?

In aquaculture production, algae in pond water that reproduce too vigorously will inevitably age and die, and the replacement of old with new is originally a normal phenomenon. However, when caused by continuous high temperatures or sudden changes in air temperature or water temperature, heavy rain, water stratification, sudden salinity changes, and so on, the mass death of algae is commonly called algae die-off. The so-called algae die-off refers to the mass or complete death of algae in the culture water body, causing the water color to suddenly become clear or even turbid.

Ponds where algae die-off occurs often have a layer of dead algae floating on the water surface (generally appearing as yellow floating matter, and some ponds also form a layer of “oil film” at the downwind outlet). The water body often becomes more viscous, with many large bubbles that do not easily dissipate for a long time, and some even have bubbles of a rather dirty earthy yellow color.

2. What effects does pond algae die-off have?

When “algae die-off” occurs, first dissolved oxygen will decrease, carbon dioxide will increase, and the pH value will drop rapidly; second, the decomposition of a large amount of dead algae will not only increase oxygen consumption but also produce ammonia nitrogen and nitrite, because the self-purifying bacteria in the pond itself cannot decompose the dead algae in time, which is even more obvious on rainy days. Third, protozoa in the water will reproduce in large numbers, inhibiting the growth of algae. Fourth, lacking the settling effect of algae, suspended matter in the water (fine dust, feces, dead algae, etc.) becomes turbid.

Algae aging leads to excessive water transparency, causing benthic moss to grow. Moss has strong photosynthesis and strongly absorbs nutrients in the water, limiting the growth of planktonic algae and causing harmful bacteria to reproduce in large numbers. Dissolved oxygen in the water body drops sharply, and ammonia nitrogen and nitrite become too high. Moreover, the pond water is clear to the bottom, which is not conducive to the habitat of cultured animals and can cause cultured animals to suffer algae toxin poisoning, hypoxia, disease, and death in severe cases.

3. How to prevent and control the occurrence of pond algae die-off?

To prevent and control pond algae die-off, pond inspections should be strengthened, changes in the water body should be monitored at all times, changes in various water quality indicators should be monitored, and appropriate management measures should be taken. Attention should always be paid to weather conditions to prevent sudden weather changes from causing algae die-off. Disinfectants, insecticides, and other chemical reagents should also be used with caution, especially algae-killing products, because improper use can easily cause mass death of algae.

In addition, microecological preparations such as Bacillus subtilis, photosynthetic bacteria, and aquaculture EM bacteria should be used regularly to regulate water, and substrate improvement should be carried out in a planned way. The timing and method of fertilizing the water should also be well controlled. Once algae die-off occurs in a pond, the aerator should be turned on immediately and used in coordination to prevent fish and shrimp from lacking oxygen.

According to the condition of the algae die-off, measures such as adding water, changing water, or using related products for conditioning should be taken. After handling algae die-off, attention should be paid to fertilizing the water, and microecological preparations should be used in coordination to regulate water quality.