i have a 60l tank it was in a tank with guppies but they never bothered with him. I had a fish with dropsy that got ate so it might of affected the betta also a guppy died a few hours later so i dont know
I agree no go area betta and guppys.
Betta's see them as competition the will even kill them.
If a fish had dropsy add a bacterial med if the fish was pecked at.