You raise a good point- there is no direct evidence that the hand sanitizer was the culprit here. For the sake of argument, let's say the hand sanitizer was the problem. If so, it raises the question- which particular sanitizer was used? The OP states only that it was 'one of the sanitizers used in stores, so industrial type,' whatever that means. Do such things contain particularly toxic substances? Possibly. Can we ever really know the culprit? Probably not, as it may be a contaminant present in one of the listed ingredients. Whatever it was, it had to be extremely potent, because with the dilution factors involved in a 55 gallon tank, the presumptive toxin had to be active in pM or even fM amounts.
Bottom line here- wash your hands before you put them in your fish tanks; it's just common sense. Would you really put your hands in a tank after you've just applied after-shave lotion or perfume? Of course not. I very much doubt that this one instance indicates that most hand sanitizers are any more toxic to our fishes that any of a whole array of substances that we may get on our hands everyday. Not a difficult problem to solve- wash your hands! And keep your kids out of your fish tanks!
