Sera ph Minus lowers the ph-value in freshwater aquariums reliably. If the pH value is higher than 7.0 and the KH value is higher than 6 ° dKH, 5 ml of Sera Sera ph Minus can be added for every 20 liters of water in the aquarium. If the pH value is 7.0 or lower, only 1 - 2 ml of Sera ph Minus can be added for every 20 liters of water.