One of my customers buys mini gerbs every other week for bud vases in her salon. I always give the girls a pill when they collect the flowers (bit embarrasing, me being a male!). Couple of weeks ago one of the girls commented that she had made up the treated water but had run out just before filling the last vase, so she used plain tap water in that one. By the end of the week, that one gerbera was flagging, but all the others were still looking good. Speaks for itself really and not hard to test it yourself the same way.