>or would you >let it be longer for bacteria. There are exceptions, but some fish-pathogenic bacteria are actually difficult to culture in-vitro. More importantly, as was mentioned during the height of the anthrax threat, there is a lower limit to the number of disease organisms needed to cause disease. Obviously when you have an outbreak of a very contagious disease like Ich or Velvet you'd want to be very careful about spreading it by passing out samples of water (especially since these two diseases have an encysted reproductive phase). I'm just saying that, statistically, when plants are taken from tanks of fish that are even moderately healthy there is only a low probability of passing a disease along. Most of these parasites work very hard at finding and staying on fish. There are differences for each disease of course. Steev