Why can't you vacuum or brush? My water is still cool (haven't measured the temp) and I've been vacuuming for awhile now. Probably the first time was sometime at the end of March and I doubt my water was any warmer than 55 at that point.

By the way --- to save on your reagents, use the 10ml water sample instead of the 25ml sample. A testing margin of 0.5 is just fine and it isn't worth the extra reagents to get a 0.2 margin.