I think DBT might have a weaker immune system because im pretty sure the double tailing is really just a genetic deformity... doesnt look right to me. My DBT got fin rot right after i got him and i could not fix him! he died about 5 months later with nearly 50% of his fins missing... no idea why or how he died, kept his water clean and everything... w/e..
Its sad about that Red VT! You should get him a larger vase or tank, and maybe tell him to clean it more often! At least once a week! tahts not much to ask!