Yea, sorry to hear man. If I were you, Id read up on this site about filtration before I tried another lungfish, it sounds like the problem here was the ammonia and nitrites that you mentioned. Any ammonia at all can be deadly, and trace amounts of nitrites can be just as deadly if not taken care of. What kind of filter was it? You said charcoal, but what brand? And you need to focus on biological, not chemical, filtration next time. Just look around this site and youll pick it up - I learned a lot just in looking around this site the last few months, its really helpful. All in all, sorry to hear, and just do some more research and you will be ready to try another lungfish.