I was going to add on to the cloudy star-san thread, but I think this is a little different.
I like to us sani-clean (the no-foam version of star-san) for certain applications, but I have noticed that if it sits for a few days in a covered bucket, floating coagulated parts form. I am not sure what it is, but I don't like it. They mostly seem to settle down to the bottom of the bucket, but are easily roused. The pH is still in the appropriate range for effective sanitation, but I would like to know what this stuff is, and if it affects the normal usage of the product.