I bought a soft-pack of Citrin stop bath from Macodirect (http://www.macodirect.de/citrin-citrostopbr330ml-softpack-p-2196.html). According to the label it has an indicator, but which colours it will change from and to was not specified. When I first mixed it it had a clear purple colour. After a three rolls and a week in a plastic bottled-water bottle it has paled noticeably. Surely three rolls can't deplete 1,5 liters of stop bath? The bathroom floor is not particularly warm, a tray of water stored next to the chem bottles with a thermometer in it showed 20-22 C all week. Is the stop bath bad? Is this colour change normal even if not depleted, or does stop bath go bad in a week even if barely used?