going for an amazon basin aquarium set-up, the lush Amazon river is just great, ain't it?
So, you're planning a relatively still, soft, low pH environment with lots of plants, bogwood, etc? Are you considering black water or just the mildly golden effect of leaching tannins?
If you're truly loving the Amazonian basin biotope the best loaches I could think of that would do well in such a set up are khuli loaches. Some are very hard to source, however, and often difficult to ID with absolute certainty. They are not native to the amazon, so having loaches depends on how true to the actual biotope you intend to stay.
For an amazon tank my personal preference would be a nice shoal of discus or altums, a
large school of smaller, colorful species and a couple of peaceful bottom dwellers. It would have a sandy substrate, be heavily planted, with some open areas for the discus, and a bunch of interesting wood specimens (Australian ironwood is perfect for aquariums).
With a 500l (130g) tank, you have a lot of options. Can we see a pic of the tank? And what are the dimensions? Botia species prefer a long footprint with room to race, angels, discus, altums need a tank that is taller rather than longer.
Another thing to keep in mind is that while your tank may be cycled at 6-7 weeks, it is not what I'd consider a 'mature' tank and many of the fish I've suggested, including most loach species, are best introduced to mature tanks with well developed biofilm, biofilter, and ecosystems - including some types of natural algae. The youngest I'd go for saying a tank is fully mature is about 3 months.
Have you been keeping fish for a long time and this is a new venture for you, or is this your first foray into fishkeeping, or something inbetween?
Have a look here:
http://fish.mongabay.com/biotope_cardinals_discus.htm
Great pics of biotopes of a few types as well as links to other places you can find info.
And here:
http://www.aquabotanic.com/gallery.htm where you can see examples of some gorgeous tanks like these:
