exodons are a coin toss, they can kill young piranha and adult piranha can eat them. plus they are uselly 5-7 bucks a pop and you have to shoal them. 40 bucks for a try is a bit much. i have had shaol of 5 bala shark that are doing good(to fast for the piranha), 3 clown loachs(i dont know why they are still alive), breeding shoals of guppys and mollies(so small the piranha dont bother), and a pleco that although he gets bit often they never really harm him and 2 chinese algea eaters(mean little bastards, they chase the piranha). In the end most things are trial and error. My fish will put up with some but kill others as soon as they hit the water. you have too try and see. I just wouldnt spend to much on what might end up being lunch, or worse make lunch of your red bellys
quick answer: nothing permanently. i've tried several different fish. none of them worked, and i lost 2 jardinis , lots of tigerbarbs, an archer fish, a bichir, and some other fish.
so its not worth it, keep your tank P only.
I had a 1 Pleco with 12 of my P's for 4 mos. until they decided to go and eat him 1 day. I then bought a bigger Pleco to put with my P's for over 6 mos. now.. They don't even bother him, even when the Pleco smacks them in the face with his tail.. lol