Is that payara a Scomb or a Raph?? I have a friend that had a foot and a half raphiodon in a 200 gal and it did that same thing. teeth out the side. I know for a fact he has good water conditions in his tanks and still did it. he told me that it was his favorite fish in the world and that the raph's are also sensitive to tank size. after it reached a foot, it never left one corner. started to rub and ended up having the snaggle tooth look yours does. he told me his did it to tell him the fish needed a bigger home. maybe this could be the reason yours is doing it. I do know that scombs and raphs are sensitive to tank mates as well and they like to be left alone. if stress is the factor from tankmates, might need to move him to a same sized or larger tank with fish that wont bother or try to pick territories with your payara. just my input...