<p num="59">FIELD: biotechnology.</p> <p num="60">SUBSTANCE: invention relates to biotechnology, in particular to algaecides based on organic acids – metabolites of aquatic plants, used for treatment of artificial aquatic ecosystems – aquariums, aquaculture pools, in order to selectively inhibit bloom caused by cyanobacteria and green algae and maintain ecosystem development. Described is an algaecide for selective suppression of flowering caused by cyanobacteria and green algae in artificial aquatic ecosystems, characterized by that the composition includes gallic, tetradecanoic, heptanoic, octanoic acids and ethanol, and using a natural mechanism of allelopathy to control development of cyanobacteria and green algae, in the following concentrations, (g/l) (% of active compound): gallic acid C<sub>7</sub>H<sub>6</sub>O<sub>5</sub> (Gallic acid) – 70 (25); tetradecanoic acid C<sub>14</sub>H<sub>28</sub>O<sub>2</sub> (Tetradecanoic acid) – 70 (25); heptanoic acid C<sub>7</sub>H<sub>14</sub>O<sub>2</sub> (Hep
