Forgive my ignorance since I am just getting back into fishkeeping, but it can also be frustrating when there is so much conflicting information out there.
My 20 g. contains 4 ADFs, 5 cardinal tetras, and a betta. They all get along very well. I know betta's can be tricky, but mine has been fine. The frogs have never gone after him. In fact, sometimes they bump into him on their way to the top of the tank and he doesn't seem to mind at all. They've never gone after his fins. He nipped at their toes when I first introduced him to the tank, but I think he may have thought they were worms since he'd probably never seen ADFs before.
Anyway, I recently added a mystery snail to the mix. Nothing I've read indicated that there would be compatibility issues. Two different Petsmart clerks agreed that the combination would be fine. Yes, I know bettas often have issues with other fish, but I also know that bettas have a wide range of temperment and lots of people have not had problems with this combination.
When I first added my snail and it started exploring the tank the ADFs went after its antennae (thought they might be worms, perhaps?). The snail "clammed up." The betta then spent the day hovering around it. If the snail started to open his door, the betta would nip at it. Seems weird that the betta would stalk the snail like that.
Has anyone had any experience with this? Advice? Right now I have a divider in the tank with the frogs and betta on one side and the tetras and snail on the other. The snail is currently happily exploring his side of the tank. Do you think this will have to be the permanent solution?