By the time anyone could post a reply, all actions will be taken. I went to feed our fish (see profile for list) and then did a quick fish head count to make sure everyone was there. Well, I noticed only 2 of 4 neon tets which wasn't a big deal, because sometimes, though it's rare, fish will hide in the castle. Then I noticed that the goldfish (no, I didn't put it there) had something in his mouth, that looked strangly like a tet fin. I netted him and looked in his mouth but didn't see anything. I moved the castle and no tets came out, but I counted the general population again, and this time saw 3 tets. I looked closer and wished I hadn't. Our total fish death toll is now four.
I read that goldfish can survive in non-oxy'ed water and will put him in a divided tank with a betta on the other side. I don't really care, as I DIDN'T BUY HIM! I know it sounds cruel, but I won't put him back in the big tank, because I don't want to lose anymore. Any advise you could give would be helpful.