Use of a biocide composition having a pH in the range from pH 1 to pH 5, comprising: a) from 0.25 to 20 wt% of 5-chloro-2-methyl-4-isothiazolin-3-one having a 2-methyl-4-isothiazolin-3-one content in the range from 0 to 2 wt%, based on the total fraction of the 5-chloro-2-methyl-4-isothiazolin-3-one, b) a solvent, and at least one stabilizer selected from the group c), d), e) and f): c) from 0.1 to 25 wt% of a metal nitrate d) from 0.1 to 500 ppm of copper ions (Cu 2+) e) from 5 ppm to 10 000 ppm of an oxidizing agent f) from 5 ppm to 1000 ppm of 2-bromo-2-nitropropane-1,3-diol and/or formaldehyde, for reducing microbial infestation of a product, characterized in that the product is selected from the group consisting of paints, interior paints, varnishes, stains, renders, interior plasters, polymer emulsions, latices, polymer dispersions, lignosulfonates, chalk suspensions, mineral slurries, ceramic masses, adhesives, sealants, products containing casein, products containing starch, bitumen emulsions, surfactant solutions, fuels, cleaning products, pigment pastes and pigment dispersions, liquid inks, lithographic liquids, thickeners, cosmetic products, toilet articles, water circuits, liquids in paper processing, liquids in leather production, liquids in textile production, drilling and cutting oils, hydraulic fluids, and cooling lubricants. a) from 0.25 to 20 wt% of 5-chloro-2-methyl-4-isothiazolin-3-one having a 2-methyl-4-isothiazolin-3-one content in the range from 0 to 2 wt%, based on the total fraction of the 5-chloro-2-methyl-4-isothiazolin-3-one, b) a solvent, and at least one stabilizer selected from the group c), d), e) and f): c) from 0.1 to 25 wt% of a metal nitrate d) from 0.1 to 500 ppm of copper ions (Cu 2+) e) from 5 ppm to 10 000 ppm of an oxidizing agent f) from 5 ppm to 1000 ppm of 2-bromo-2-nitropropane-1,3-diol and/or formaldehyde, for reducing microbial infestation of a product, characterized in that the product is selected from the group consisting of paints, interior paints, varnishes, stains, renders, interior plasters, polymer emulsions, latices, polymer dispersions, lignosulfonates, chalk suspensions, mineral slurries, ceramic masses, adhesives, sealants, products containing casein, products containing starch, bitumen emulsions, surfactant solutions, fuels, cleaning products, pigment pastes and pigment dispersions, liquid inks, lithographic liquids, thickeners, cosmetic products, toilet articles, water circuits, liquids in paper processing, liquids in leather production, liquids in textile production, drilling and cutting oils, hydraulic fluids, and cooling lubricants. at least one stabilizer selected from the group c), d), e) and f): c) from 0.1 to 25 wt% of a metal nitrate d) from 0.1 to 500 ppm of copper ions (Cu 2+) e) from 5 ppm to 10 000 ppm of an oxidizing agent f) from 5 ppm to 1000 ppm of 2-bromo-2-nitropropane-1,3-diol and/or formaldehyde, c) from 0.1 to 25 wt% of a metal nitrate d) from 0.1 to 500 ppm of copper ions (Cu 2+) e) from 5 ppm to 10 000 ppm of an oxidizing agent f) from 5 ppm to 1000 ppm of 2-bromo-2-nitropropane-1,3-diol and/or formaldehyde, for reducing microbial infestation of a product, characterized in that the product is selected from the group consisting of paints, interior paints, varnishes, stains, renders, interior plasters, polymer emulsions, latices, polymer dispersions, lignosulfonates, chalk suspensions, mineral slurries, ceramic masses, adhesives, sealants, products containing casein, products containing starch, bitumen emulsions, surfactant solutions, fuels, cleaning products, pigment pastes and pigment dispersions, liquid inks, lithographic liquids, thickeners, cosmetic products, toilet articles, water circuits, liquids in paper processing, liquids in leather production, liquids in textile production, drilling and cutting oils, hydraulic fluids, and cooling lubricants.