The foaming tendency of aqueous systems containing biocidal quaternary ammonium and/or phosphonium compounds is reduced by addition of anionic surfactants in a molar ratio of anionic surfactant(s) to quaternary compound(s) of from 0.001 to 0.2. A preferred application of the aqueous systems according to the invention is in swimming pool or spa waters as algaecides.本發明藉著以從0.001到0.2之陰離子表面活性劑(們)對四級化合物(們)的莫耳比例,添加陰離子表面活性劑,降低含有殺生物之四級銨及/或四級鏻化合物之水性系統的起泡傾向。根據本發明之水性系統的較佳應用是在游泳池或水療(spa)用水中作為殺藻劑。
