Water is not just water and especially not tap water!
First of all, your water should be clean and free of ammonia, nitrite and chlorine! Have you thought about the right filtering that fits the size of your aquarium and the number and species of fish?
It is also equally important that you strive to add to your aquarium water the organic minerals, trace elements, tannins and fulvic acids found in the waters of the Amazon. Both wild-caught and cultured fish depend on the presence of these substances, in order to transpose and digest their food. You will find a comprehensive article "The waters of the Amazon", which deal with this issue in detail, in our Article archive at the top of the front page.