A correct Gh value is between 8 and 12 dH. Too low a value quickly produces a lot of algae growth, oxygen plants can also wear out and fish health can be affected. A hardness lower than 7 no longer increases itself and the biological balance falls away. So test the water regularly and add appropriate minerals if necessary. In winter, make sure your Gh is at least 12 dH. 1000ml Gh+ increases...