Waters used in Experiment 1 differed in two major characteristics:
First, WARU water contained appreciable DOM while SNARC water
did not. Second, SNARC water contained higher levels of calcium and
magnesium (cations contributing to hardness) than WARU water. Either
parameter could have accounted for the large difference in fish
mortality rates seen in Experiment 1. Furthermore, the in vitro experiment
indicated that humic substances at the levels found in WARU
water were not directly toxic to F. columnare.