QUEREX oak bark extract. QUEREX is the extract from oak bark. It helps prepare the so called “black water”. Hummus compounds and tannins slightly acidify the water, lowering its hardness and giving a characteristic amber colour. In addition, they inhibit the development of fungi and bacteria, lowering the risk of infections. Only such conditions guarantee intensive coloration, reproduction, excellent health and vitality. We recommend using QUEREX in tanks with discus, angelfish, South American cichlids, characins, Colisa, Corydoras etc. To strengthen the effect, use QUEREX together with TORFIN COMPLEX.