Hi Lilia and Dionigi, tea as softener seems a little exotic. But i heard of benefits of black tea in breeding congo tetras (Phenacogrammus interruptus). These delicate tetras are very diffucult to breed because their eggs need a longer time to develop than most other tetra eggs do. In most cases the eggs get infected by bacteria or funghi and even if fry comes up there is often a high percentage of belly sliders. Tea helps: Tea is used in breeding as sterilizer as well as softener and acid source for lower pH. Additionaly should be added that fresh tea is blamed to be agressive and may damage fish - water must age a little 3 or 4 days. Dosage ??? (not sure: about 1 cup of tea per 10 L). Must admit no experiences in it. Thomas