How to stop a bully oscar

[ALEX1989]

Hi every one. I am a beginner when it comes to fish and aquarium so could use a little help. I had bought a flowerhorn and a small oscar a birchir and a Loricariidae. It ended up that the flowerhorn (which is smaller) attacked my Oscar and made it hide all the time, then I got a big Oscar and there was complete peace. Then they were moved to a larger aquarium (530l) But the big one seemed stressed and swam back and forth all the time and the little Oscar tried and attacked it, maybe it was because it was weak due to stress. I laid a giant branch where it swam and turned into a cave, but now I have created a monster ? now it has gone from and be completely peaceful to and become aggressive and chases the little one into the cave. But funny enough, the big one does not touch my flowerhorn at all. If there is cause for concern, I have to give it time, what do you do? I removed the branch when I thought it would change it, but only slightly. It started and does exactly the same as before but this time it sees the little Oscar and then it gets hunted again