Guppy Origins and Environment
(2) Clear or blue water rivers are tributaries which flow through ancient Brazilian and Guyana rock beds where little sediment is released into the rivers. The water of these rivers is very clear and allows plant growth. Clearwater rivers have a pH of 6.9-7.5 and a water hardness of 5-12 dH. The Rio Xingu and the Rio Tocantins are such rivers.
(3) Blackwater rivers are nutrient poor and tea or black in color from the tanic acid released from decaying vegetation. Blackwater has been compared to distilled water due to its lack of dissolved minerals. Blackwater rivers are acidic and have a pH of 6.0 with little measurable water hardness (0 dH). The Rio Negro is the most famous of the blackwater rivers.