air likes to take the path of least resistance. so in order to run multiple objects off the same pump takes multiple valves, and some fiddling to get things balanced out. for only a few small tanks, just run 1 pump per tank, life is easier that way.
definately find where its coming from. i dont worry about the fish so much as they arent likely going to become a current path, you however can most definately become a path to ground if you stick your hand in a tank with electricity in it.
repashy is supposed to be about like jello. well for me a very stiff jello( i do 1 part repashy to 3 parts hot water). you can also feed repashy powder straight into a tank for small fry, just dont use too much.
to be honest, i do survival of the fittest. baby swordtails tend to do okay in a community tank. they will likely be fine where you have them for a week or two while they put on a little size.