Originally Posted by PhlyanPan
I've been told it keeps as long as the PH remains within a specified limit. (though I can't remember what that limit is) I think as long as you keep it in a closed container you're fine for quite a long time.
So long as the PH is below 3, it's still effective.
Many people find it goes cloudy immediately after mixing, due to minerals in their tap water. I can't remember who, but somebody on the forum did some really extensive testing, and found that the PH stayed well below 3 for much longer than expected, long after it had gone cloudy.
Ah, here it is! Star San cloudiness lab report