I've never heard anyone comment on how long PBW is good for when mixed up. I usually mix up 20 gallons and use it for multiple brews that day then write it off. Can I keep it 2 days? 3? A week? As long as its not nasty? I can put a lid on it. I don't feel the need to keep it over a week but it would be nice to use it for several days in a row. Does it lose effectiveness? I know it tends to remain slippery feeling and alkaline.