Agreed. Poor babies. It most likely wasn't the fish that did them in. My chicks/chickens love fish, crab, shrimp, ect. They even eat the shrimp shells. If those chicks were living outside in a birdcage, were they protected from the elements? Since you were feeding birdseed, were you giving them grit? Why were you adding bleach to their water, to keep sludge down, kill germs? Changing the water everyday and cleaning the waterer often would do the same thing. Or if you must add something, add some apple cider vinegar. Depending on your weather, they could have still needed supplemental heat. I can see lots of reasons for your chicks to die, but the fish isn't one of them. Do some research, better luck next time
Nikki