120 gallon cichlid tank

[Bertie]

That would probably be a little easier on the tank bioload-wise. Although personally I think you would be okay with the Oscar as well if you really wanted it. You are going to get plenty of differing opinions in an online forum, it's your job to sift through them and decide what to follow. Is RD wrong about a single Oscar in a 120 gallon needing an 80% water change every week? No, i'm sure if you followed his advice you would have a healthy and happy Oscar. Would you also be able to keep the Oscar with some tankmates, and do a 50% water change, and keep nitrates within an acceptable level? I believe you would.
What I'm trying to say is that aside from some things like consensuses about minimum tank size for a species, there is a lot of variability to what "will work". It's hard to just give you a cookie cutter stock and amount of maintenance and guarantee the fish won't kill each other or the tank won't get dirty.
You have some species listed that won't outgrow your tank. I'd say get what you want stocking wise, and give it a shot. Adjust maintenance and stocking as you see fit.

I think I will just go for what I want and see If it works

 

[Bertie]

Thanks for all the help

 

[Rocksor]

What about if I got rid of the oscar and did a chocolate with some geophagus or guianacara and some dithers

That would work with something like giant danios or similar sized dithers; buenos aires tetras if you want to stay in South America. I would choose smaller geophagus like red head tapajos. The guianacara would also work. They do make a nice color contrast to the chocolate.

Remember to keep nitrates below 20ppm every day. If you can keep it lower, even better. Get a liquid test kit if you don't already have one and a Python No Spill water changer.

In my experience a 12" oscar need at least 60 gallons of water changed every week to keep nitrates below 20ppm everyday. The oscar was fed only 4 days out of the week, and only once at feeding days. If I fed the oscar more, I had to increase my water changes.

 

[seanh]

I think I will just go for what I want and see If it works

Absolutely, trial and error to see what works.

I personally wouldnt have a fish over 10/12 inch in a 4ft tank (the oscar). I just dont think that would be aesthetically pleasing as it will look too cramped. But each to their own.