Oak bark extract intended to create the so-called black water. It contains humus compounds and tannins which lower the pH value, the hardness of the water and give it the characteristic amber colour. They also inhibit the development of fungus and bacteria, hence protect against dangerous infections. They create perfect conditions for the fish to develop beautiful coloration, to pair and spawn readily and keep them in excellent health and condition. QUEREX is recommended for aquaria with discus, angelfish, South American cichlids, characins, gouramis and cory catfish. The best way to intensify the activity of QUEREX is to use it together with TORFIN.