Back when I was young and ignorant and full of my own ideas i tried keeping a sveni pike, 1 rbp, and a pinktailed chalceus in a growout tank 20 gallon all 1-2 inches. The sveni and the rbp were cool with each other but the rbp tried to take chunks out of the chalceus's tail and the chalceus repelled the attacks for awhile then took the beating so I exchanged him for a dovii at 1.5 inches. The feisty lil bugger took dominance over the rbp but couldn't beat the pike. They lived in harmony for about 6 months until they started to mature, the dovii started turning grayish blue and the piranha developed some red on his belly and some fins. Then one day they got into a huge fight after feeding (most fights happen after this I noticed) and the dovii as usual whupped the rbp's a** . But the rbp was relentless and they fought hard on and off for three days straight and each day I thought it would be over the next day. finally I came home to see my (now 4inches) dovii with a hole in his belly and his tail chopped off floating at the surface. The rbp had some damage but healed extremely quickly. Just thought it would be nice to add to the thread, it was a pretty cool tank tho I gotta admit, I'm always tempted to try it again even tho it isn't the best idea lol