Hardcore necro, my apologies but I figure most folks won't be active and those who are might like a continuation. I just went to a local pet store two days ago to get emergency mice for a snake and I saw a 10" oscar sitting in a 10g tank, looking super miserable with 2x dead danios in front of em, apparently the store staff thought they would be good meal choices. He was sitting on the bottom, struggling, you could tell he had a day or two with these folks before he was done. Labeled as "Charlie" the 3 year old surrender, a couple brought him in and said with covid they couldn't care for the fish. Texted my wife, she said "no" immediately, sent her a picture and she called. 10 minutes later I have an oscar named Charlie in a bucket.
Relation to this post and excuse for my necro: I added Charlie into my established tank and initially my ~3 year old chocolate didn't pay him any mind at all but within a half hour he was on him. The chocolate has spent roughly 36 hours trying to engage with the oscar who just retreats, at one point the chocolate was trying to lock lips and the oscar literally turned tail and ran. I've rearranged the tank and it's 150g. All I've got in here other than these guys are a handful of cory cats, a few rainbows, a small female convict and a banded leporinus. If anyone of you guys or gals are still around, do you think it'll subside? I've never introduced another adult fish, I've always grown out my own.

(Rocks are a demarcation line, switches to gravel/sand then back to sand on the far side where I've got tunnels plenty large enough for both and unobstructed but they hang out with the fake plants or rip up my real ones)