this is a kinda dumb question; but here it goes; I 've kept fish for years; but had never owned tin foild; well yesterday I bought my first 4 tin foils ever 4x 6"ers well I put them in my dat tank and the dats really didnt care much for them; well the dats did the usual thing everytime I introduce a new fish but nothing really serious. Anyway so the I drip acclimated the tin foils for about an hour almost and then put them in the tank; they seemed fine except for the fact that they were breathing a little heavily; which I thought was normal becuse I just put them in a new tank. Anyway a few hours go by and the tin foils were swimming around the tank. So I decided to do a 25% water change later in the evening; well after I did this an hour later 3 of my for tin foils were dead; what happend???