It's funny you plan on putting a firemouth with your oscar; that's what I have with mine. They're in a 65 growout (this because I don't have the room for a 150 yet) for now, peaceful thankfully. They will swim near each other and kind check out what the other one is doing, but they never chase each other or stay hiding from each other. The firemouth is actually timid with me, but because my oscar gets all excited to see me, he seems to be getting braver seeing his friend isn't scared.
@jclyde: I didn't mean the example of a 20 vs a 75, maybe like a 40 or something in comparing water changes; so it wouldn't get as bad in the smaller tank in comparison, ya know? Also, with my 65 I noticed that compared to before, occasionally bits of food get shunted away from the oscar before he can get to them, compared to the smaller tank he had before. Mind you, it's an easy adjustment where i just drop 2 pellets at a time versus all 7-8, but that's just an example. Tue, oscars are super food-oriented, but I'm sure other fish may not be as quick to find stuff.
@jclyde: I didn't mean the example of a 20 vs a 75, maybe like a 40 or something in comparing water changes; so it wouldn't get as bad in the smaller tank in comparison, ya know? Also, with my 65 I noticed that compared to before, occasionally bits of food get shunted away from the oscar before he can get to them, compared to the smaller tank he had before. Mind you, it's an easy adjustment where i just drop 2 pellets at a time versus all 7-8, but that's just an example. Tue, oscars are super food-oriented, but I'm sure other fish may not be as quick to find stuff.