I have a goldfish that's approximately 8-10 years old. I got her and another goldfish about 8 months ago. Before that she wasn't cared for all that well. The other goldfish sadly passed away shortly after i got her and showed the same symptoms this one does now. A month ago my goldfish started to almost gasp for air on the top of the water surface.So i imminently thought it was either an ammonia build up or she was not getting enough air. The ammonia build up was highly unlikely since i do a 20% water change on her tank once a week.PS she's quite a messy fish. But i did test her water and the parameters were normal. I bought her an air stone, and i better positioned her filter. Now in a span of 2 days she barely moves and just lets the flow of the water move her. She also tries to position herself between plants and just lays there. Today she didn't even eat. ABOUT THE TANK I do a weekly 20% water change. (I use a water de chlorinator) I keep her water a bit colder than room temperature. Tank size 55L Please if anyone could help me out in what i could be doing wrong i'd really appreciate the help. It breaks my heart to see her like this.