I actually tried a single male krib in my community tank and he was more aggressive than the GBR I had in their before him. He seemed fine with the tetras and danios at first, then one day he wouldnt let any other fish hang near that bottom. As a result, he disrupted the balance of the tank and my zebra danios became fin nippers to the cardinal tetra.. I called the LFS where I bought the krib and they let me exchange him for another Ram.. After that switch, my tank became peaceful again and the danios stopped nipping.. Interesting shift of behaviors when there's a bully present or removed.