i have had an oscar in with my reds for about 3 months but i sold him as he would try and fight with the reds on occasion which he always lost ,he would usually have tail nips and one day tried to lock mouths with a red and lost part of a lip which is why i sold him
i have tried other fish with reds ie cons but got rid as it just does not work, imo a plec is the only thing you can have in a red tank i have onenow and it is ok so far " 1 year now
I think it can be done, I have a severum with my piranhas, but it is bigger than them, and was loads bigger when I got the piranhas which were just small at the time, the severum is about 7-8".
It has worked since march.
I've had two kribensis cichlids with my reds, and all went well until the couple decided to pair up and form a territory. The male became very agressive towards the reds and eventually got killed.
So now I have a kribensis widow in my tank...
I dont see a point to it. I would add different typs of pygos if you want a little variety. I know not everyone agrees with a mixed tank but I like the look. If you do decide to, I would take the p's out, rearange the tank, add the oscar and give him a little time to check out the tank before you add the p's back in.