What to do when a fantail fish has swim-bladder?

Swim bladder is not contagious at all. It is not a disease, parasite, or anything like that. I would move him back. It sounds like your fish is constipated. Also, the plants do not take out oxygen. They breath in Co2 and the fish breath in oxygen. So that was completely useless. Keep trying the peas. It cures it for a time.