When yellow water is beautiful
This is George Farmer's Evolution Aqua Aquascaper 600 aquarium set up for pentazona barbs, driftwood and Bucephalandra plants. It uses a blend of Tannin Aquatics "botanicals" (visible on the sandbed) to create the yellow/orange water color, replicating the acidic Southeast Asian habitat of pentazona barbs.
In nature, the chemistry of freshwater is often altered by decaying organic compounds such as from driftwood, fallen leaves, and other plant matter. These organics leech tannins and humic compounds into the water while lowering the pH (usually in the range of 5 to 7). Furthermore, these acidic substances impart color to the water in the same way tea leaves make water yellow/orange/brown.
The water isn't "dirty," just colored and acidified by plant matter. This is a perfectly natural environment for many cichlids (e.g. discus, angelfish), barbs, tetras, et al. And the discoloration conveys a mystical beauty to an aquascape so don't be afraid of yellow water (sometimes referred to as "blackwater") in your next freshwater setup.