Betta fin rot

[Bambithegirl]

Hi All, Well this is what Matisse looks like. Still no change in behaviour and appetite but his fins are just looking so terrible. Ive treated him once with tetra general tonic which killed one of my plants. Ive been adding rooibos teabags to the water too as many people in SA say it helps. I clean his tank every week religiously. He is the only fish in the tank. Is he just always going to have this problem? I have aquarium salt but Im reluctant to use it because of mixed comments about it, plus the plants will have to be removed. Im also not sure that it will stop it from happening in the future. What is causing this? Is he bored? Should I get more plants, or other fish? I have some dwarf cories waiting at the pet shop, i didnt want to get them until he is better but maybe I should?