Help I've got a broken fish tank filter!?

tetras are an incredibly hard fish to look after depending on what kind, you tank should have started the fish cycle before adding any fish (look up the fish cycle), the fish died because the cycle hadn't been started and the tank not set up for long enough, bob wont survive long if you don't get it all sorted and very fast. you needed to put a lot more detail into your extra info bit; what size tank?, what filter?, other fish? and so on.