black marks

Question
Hey i have a 10 gal tank with a black moore, an Oranda, and a gold dojo loach. i know the tank is two small and I'm trying to get a bigger one, the tank is only about 45 days old and i have had the fish for about the same amount of time. anyway i found out how dirty gold fish are real quick but i missed a few water changes recently and i am assuming that the ammonia levels got a little high.  i recently noticed on my Oranda's back left fin at the edge was getting darker almost turning black. i thought maybe fin rot but i dont think it match's the symptoms. the fin is staying perfectly intact just turning darker. and now the right back fin has a small dark mark on it. so i read somewhere that this could be actuall burns from the high levels of amonia. have you heard anything about that. and what else could it be? i just did a 50% water change and i hope it clears up. also the fish is acting perfectly healthy. still first to find food and is still stealing meals from the loach. still a very energetic goldfish.

Answer
I have never heard of the ammonia level actually burning the fish; however, I have heard of the fish acting fatigued and not eating and developing diseases/parasites in response to ammonia. I suggest that if the fish are all acting normal, eating, swimming normal, all fins are up, and overall seem to be in normal health, the ammonia is probably not a big problem. However, this does not mean to not try and make up for the water changes, which I have read you have already done. As for the fish, I am not sure...it is a puzzling condition. I would have first said something like fin rot or a fungus but that would involve a fuzzy patch and would affect the fishes behavior. Other than a disease I am not sure of what it could be. It could not be an injury, as this would also affect the fishes behavior. I would make sure it is not fuzzy or make sure it does not continue to spread all over the fishes body, if any of these things happen it is a fungus and needs to be treated. Also, just because the fish is acting normal now does not mean it will be normal in a few hours. Sometimes the diseases and parasites tend to have sudden attacks. Although, do not treat the fish unless you are positive it has a disease or parasite. Look at the fish again and see if you can see a fuzziness on the patches and keep track of the patches to see if they spread. Unless behavior or physical issues changes and worsen, I suggest keeping a close eye on the fish to see its progress. Other than these ideas I do not know what else it could be. Let me know if you need more help. I hope this helps.