If you have frogs, I would go light on the salt (if you use any at all); they are much more sensitive to salinity than bettas are. The frogs generally will not cause problems for the betta, but the betta may torment the frogs. For the most part, my betta and dwarf frog get along; though my betta can be a bit of a bully, the frog usually ignores him or flees (she has several hiding places; sometimes even I can't find her!). The only other thing I can think of is feeding. If I don't feed my frog carefully, the betta will eat all of her food; he is a better scavenger (dwarf frogs have very poor sight, and sometimes I think mine is a little slower than most). I personally hold food in a pair of tweezers and offer it to her (still looking for a better method); some have recommended using turkey basters or eye droppers to feed dwarf frogs.