Solid disinfectant dosage forms having a peroxy activator and a peroxy compound are provided. The dosage form can be selected so that addition of the dosage form to a predetermined quantity of water produces a disinfectant solution containing peracetic acid in a concentration of at least about 1000 ppm. The dosage form can include a colour indicator arranged to provide a first colour signal when the concentration of peracetic acid is lower than about 1000 ppm and a second colour signal when the concentration is higher than about 1000 ppm and a third colour signal when the concentration falls below about 1000 ppm. The peroxy compound can be selected from the group consisting of sodium percarbonate, ammonium persulphate, calcium percarbonate, magnesium percarbonate, sodium perborate, sodium persulfate, sodium perphosphate and mixtures thereof.
