In all honesty, I don't think there is such a thing as a south american/amazon biotope.
Hard scape may be accurate at times, but I don't think many of the fish will ever meet each other in the wild, or live in an environment that is like the scape. Theres just too much variety and diversity.
Best to pick part of the river/region and try copy that, like a pool cut off from the river, or just have an empty, dirty tank and say its part of the amazon.
I did see on tv, a large pool/lake that was crystal clear and hard heaps of fish and plants... Might see if I can find it.