The first thing about most Amazonian biotopes is that for the majority of the year there are no substrate rooted aquatic plants, the murky water doesnt allow much light to penetrate which prevents them from growing and often the pH is so acidic that it burns the leaves!
There are 3 main distinct biotopes in the amazon basin, blackwater, white water and Oxbow lakes
Blackwater flows out of jungle streams and as the name suggests is heavy with tannins from rotting vegetation and fallen leaves and trees which give it the colour of strong black tea, it usually has a KH of 0 and a pH in the region of 4 which doesnt allow many plants to grow. A lot of our common aquarium fish like Discus, Angelfish, dwarf Cichlids, knife fishes and many species of Characins and catfish come from this biotope which makes it one of the easiest biotopes to recreate.
A blackwater biotope tank will have a silver sand (play sand) substrate and will decorated with many pieces of bogwood which should be arranged to replicate broken tree stems at the back of the aquarium and fallen twigs and branches in the front, taller pieces can have mossy plants such as Riccia (or java moss if riccia is unavailable) tied to them near the waters surface. Floating plants such as water lettuce (Pistia stratiotes) and Salvina can also be used if desired. The water should be stained a golden brown colour through the use of peat filtration and/or a blackwater tonic to acheive a natural look. Ideally the water in the tank should be soft and acidic with a pH of 6 and a KH of 3-5, this is higher than in nature but a lot more stable for a captive enviroment.
For a variation on a blackwater biotope you can have a leaf litter zone biotope which is the same but has a 3 inch layer of beech or oak leaves used as a substrate rather than silver sand. Collect the leaves in autumn/fall and store them in a dry place until needed, before adding them to the aquarium boil them for around 10 minutes to ensure they sink and any bugs they may be carrying are dead.
White water (which incedently has nothing to do with the white water you might go rafting on) flows from mountain streams and carries huge ammounts of sediments with it which give it its milky coffee colour. The pH here is usually closer to 7 and the KH around 5 from the mineral deposits washed from the mountains. Again few substrate rooted plants can grow here as little light can penetrate the murky water. Many of the Loricarid species and larger catfish and Characins found in the hobby come from this habitat.
To recreate a white water biotope again use a silver sand substrate and pieces of bogwood arranged as they would be if they had been washed down by the current but this time rounded pebbles and river cobbles can be added as decor too as these would be washed down off of the mountain sides by the flow, the current in this type of habbitat is usually quite strong so a couple of decent sized powerheads placed at one end of the tank will replicate this.
Oxbow lakes are formed when flood waters receed at the end of the rainy season leaving large inland waterholes rich in plant and animal life. Typically the water will be gin clear as the lack of current allows sediments to settle and there is not as much tannin present as in the blackwater rivers and streams. The species present here are very diverse and changes constantly but would typically be made up of mainly Cichlids and Characins.
To replicate a oxbow lake again use a silver sand substrate and decorate with pieces of bogwood arranged as they would be found had they fallen from trees above the tank. The tank can be densly planted making use mainly of Echinodorus plants (Amazon swords) and floating plants such as water lettuce and Salvinia. The pH should be neutral and the KH 5-7 though water chemistry isnt vital here.
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