Please help me figure out why my fish is swimming in circles. I have owned my 7 cent feeder goldfish for 12 years. He is huge and has been healthy for years. I rarely have ever filtered my water over the years and would let my water get pretty dirty at times, regrettabley. I recently have begun to pay more attention to his water quality. One day I found him swimming crooked with no other signs of sickness just his odd swimming movements. Also his one fin was spasming.I added salt to his tank and immediately did a 50% water change using spring water from a natural spring that people visit to bottle water in my area. I treated the water with my usual drops and let it get to room temp and added it to the tank. He quickly got better and I was relieved. A few days later he began swimming in circles. He seems to struggle to move in motions other than in his tight circles. There is no other fish in the tank with him and I have tested for all possible water quality problems. The water seems to be perfect. There are no changes in his apperance.Please,please help me figure out how to help my old buddy. I truly love this fish.