Alex, if I am not mistaken, wate ris actually an accellerant that will speed up the curing process of superglue.

As for why it won't fall off a frag but it will fall off a fish, the frags bony skeleton is glued to a rock, nothing changes there, the fish howver, is growing new dermal tissue all the the time, along with it's slime coat, eventually, the old slime coat and skin will no longer have a firm bond to the fish, and poof... no more super glue...