As Byron had mentioned, the choice of your fish will depend on your water GH and pH.
You can check your tap water company website for the tap water analysis.
Check the water hardness and pH.
If you have low GH & pH(soft water) you can go for South American and Asian fish.
But if you have hardwater(high GH, pH), you can go for African fish and live bearers (Guppies, Mollies, Platies) or Rainbow fish.
If you have soft water:
For South American fish, you can consider a group of Earth eaters(the smaller species) such as the Guianacara species. Red Head Tapajos probably may work though some prefer to get a 6ft tank for them.
Also, keep some Tetras schooling fish that are bigger in size such as Congo Tetras, Colombian Tetras, etc.
Personally, I don't like Clown Loaches as they will grow too large and ugly when they are big.
Some info:
The husbandry of all forms of Guianacara species in the aquarium is identical. Learn more about these species.
www.tfhmagazine.com