I have been asked by several customers about sell-by dates related to chemicals. This depends on the type of chemical. Products based on detergents and water softeners, for bottle washing, and descaling chemicals have a very long shelf life because generally there are no unstable elements in the formulations.
Shelf-life becomes more of an issue when oxidising disinfectants are considered such as peracetic acid and hydrogen peroxide-based disinfectants. These materials are inherently unstable (that is partly why they work well as bacteria killers) and require stabilizers in the formulation to lengthen the shelf-life. Care should be taken in storing these materials so that the decomposition is not accelerated.
Conditions which can accelerate this are: excessive heat and light and contamination. The golden rules are therefore to store in a cool place and out of direct sunlight. The caps should never be left off, to prevent any possibility of contamination from the surroundings.
Most of these materials will retain there potency for over one year, but this is very dependent on storage conditions. The decomposition will occur slowly but gradually during the year, so if you have older stock it may be necessary to check concentrations in use and, if necessary, increase the concentration slightly to compensate for any loss.