The invention provides a method of manufacturing a stable aldehyde-surfactant complex solution wherein at least one aldehyde is added to a surfactant in a first aliquot of water, at a temperature of between 40°C to 5O°C, the aldehyde is allowed to interact with the surfactant or detergent, in a complexing reaction, for at least 15 minutes whilst maintaining the temperature between 40°C to 5O°C to produce an aldehyde-surfactant complex solution, and a second aliquot of water is added after at least 15 minutes to cool the aldehyde-surfactant complex solution to below 4O°C to stop the complexing reaction.