I put my 4" Jewels in with my wifes 5" and 10" Oscars, last night. It was interesting at first. The Jewels went after a Cory, and the big O just got between them and sat there. Then they went after a Pleco, and the big O got between them and just sat there. Then the little O started chasing them, not attacking, just chasing. After 10 minutes, the Jewels had the left side of the tank, the little O had the right side, and the big O had whatever he wanted. If the jewels went to the right side, the little O chased them back to the left side. If the little O went to the left side of the tank, the Jewels would chase him back to the right side. After a little while, the Jewels decided to stand up to the big O, as soon as he fully opened his mouth, they backed off. Now everybody is swimming freely in the tank. So now the pecking order is the little O, then the Jewels, as long as the big O allows it.