I don't know whats happening to my neon tetras! (Read All)?

Ok, I think you have cycling wrong. if you just leave a bunch of water sitting in a tank it will not cycle. You need a source of ammonia. try testing the ammoni every day and the nitrite and nitrate. The ammonia will spike and once it does back down to zero the tank is cycled, this usually takes a month or so. What are the stmtoms, what did the fish look like b4 they died??