One of my goldfish has been laying on the bottom of the tank for several days, breathing slowly. Recently his condition has been constantly going up and down, and it seems like he has swim bladder/is constipated/both.
We've already tried:
Soaking his food
Changing the water
Tetracycline worked at first, but when we stopped using it, he sank to the bottom soon after, and when we tried it again, it didn't work.
The fish is around 3 and a half years old.
He has been prone to swim bladder/constipation in past.
He is a fancy goldfish.
Ammonia is fine, nitrates are fine, ph is fine, water quality is perfect, tank is 20 gallons and there is one other fish in it (who is 4 inches).
We use flake food.
Please help, thanks!