What is the shelf life of a slightly used solution of Starsan and a moderately used solution of PBW? I just get tired of making up fresh solutions, using a third of it and then throwing them out. I know Starsan has a working pH of 3 and never use it if it is above a 3. So is that the judge for Starsan? What about PBW? Is it kinda of like dishwater or the bucket you use to the wash the car, i.e., until it has too much junk or gunk in it? Anyone have thoughts or ideas?