so I have a common goldfish that lives in a 20 gallon tank by herself with a filter and heater. Recently she has been showing signs of swim bladder disease because she wouldn’t swim properly. After feeding her peas, she would perk up right away. The past couple of days she has been very slow and not as responsive as she usually is. However, right now, she is laying at the bottom of the tank and her body is arched in a u shape barely responsive and not moving. Usually when she does this, I feed her peas and she tries to swim around to eat and eventually go back to her normal self. This time, she doesn’t seem interested. I don’t know what to do or how to treat her because I don’t even know if this issue is still swim bladder disease. Please someone help.
Your goldfish has ammonia poisoning. First aid for this is to change 50% of the water at once.
You need to change 20% of the water on day 2 and day 3, and from day 4 you need to change 10% water daily. Test the water for ammonia every day until the level is safe.
Do not feed your fish until the ammonia level is safe, and after the ammonia level is safe start feeding once every 3 days and only a little food each time.
Here is some important information you need to read: https://www.fishlore.com/NitrogenCycle.htm.
Clean your gravel to get the bioload down but do not clean the filter unless it is clogged up or have reduced waterflow. Your filter will contain important bacteria that you need to take good care of to keep your tank in biological balance.