Influence of alum on cyanobacterial blooms and water quality of earthen fish ponds

Eruption of blue-green algal blooms occurs frequently in eutrophic lakes and fish ponds, with associated unpleasant odor and horrid scums. In the present study, we conducted a pre-test experiment in 3 m³ outdoor concrete ponds to determine the optimum concentration of aluminum sulfate (alum) required for reduction of the cyanobacterial blooms without negative effect on fish growth. As a consequence, 10 mg L^?1 alum was named as the optimum concentration that was applied in 1000 m³ earthen fish ponds. Obtained results showed that Secchi disc values significantly increased from 10 to 24 cm after 14 days of alum application. Alum-treated ponds showed a reduction in total phytoplankton counts by 94 and 96 % compared to the corresponding controls after 10 and 14 days, respectively. Abundance of blue-green algae in the treated ponds was decreased by 98 % compared to the corresponding control after 14 days of alum application. Consequently, dissolved oxygen, pH, total phosphorus, orthophosphate, and chlorophyll “a” content declined significantly. Our study revealed that using 10 mg L^?1 of alum is an effective way to control cyanobacterial blooms in eutrophic waters, especially in fish ponds, without negative effect in water quality.