So I have kept 2 fantail goldfish inside of a 20 gallon long for 4 months now. My first goldfish is perfectly fine and eats and swims as she pleases. However, my other goldfish seems to always float to the top and at times tires out and just floats until the filter brings him close and pushes him. Now, I have looked up how to treat swim bladder and have fed peas to my goldfish in a bare bottom tank for 1.5 weeks. During these 1.5 weeks my goldfish was healed and swam normally. However, the week after I started feeding pellets it seems he can't swim in the middle or bottom of the tank and always remain around the top. He has no trouble eating at all. I'm really confused as to what the problem is as my other goldfish is healthy, I'm wondering if it's genetics or something because I've been trying to heal him for 3 months with only temporary success.