The selected compounds were tested in triplicates at a series of geometrically decreasing concentrations: 1000, 100, 10, 1, and 0.1 mg dm -3 . For 1-dodecylquininium bromide, due to its low solubility in water and expected high toxicity, a different series was used: 10, 1, 0.1, 0.01, and 0.001 mg dm -3 . The absorbance at 688 nm was tested for each sample using 10 cm-long glass cuvettes, and the measurements were conducted at the start of the experiment and after 72 hours. The contents of all test vessels were mixed and illuminated continuously during the test, and their position was randomized to achieve similar levels of illumination for each sample throughout the experiment. The tests were conducted at 22-23 °C. The rate of algae growth inhibition was calculated according to the following equation: