I am fairly new to the keeping of aquatic pets and will admit to only have begun to get into the hobby three and a half months ago. I researched species, tanks, possible problems, etc and then purchased a starter tank with basic filter and some ornaments. In this tank I now have an axolotl (male), an African Clawed Frog (female), a Blackmoor (female) and the most recent addition, a Bubble Eye Goldfish (gender unknown). It is only recently that the Bubble Eye Goldfish has developed signs of what looks similar to Ammonia Burn but I cannot be sure as its tank mates have no symptoms or sign of this whatsoever. It started off being on its left anal fin but has since started to appear on the right anal fin, the caudal fin, and pectoral fin. The black streaks appeared suddenly over a period of only 2 weeks. I have had the fish for only 3 and a half weeks at most. Its gills and scales are healthy as far as I can tell and it is eating well, etc. In terms of tank maintenance, I use dechlorinator and Accuclear and do a 50% water change every two weeks, though today I had to clean the tank out completely as a thick slime had formed and the filter and Accuclear were having no effect. I rarely clean the whole tank out as I am aware this can stress the fish out. I am taking some water to the aquarium for testing tomorrow. Please help and give me some advice. Has anyone else had this issue?