sera pH-minus 

sera pH-minus safely lowers the pH value in freshwater aquariums. In case of pH values above 7.0 and KH values above 6°dKH add 5 ml sera pH-minus per 20 liters (5 gal.) of aquarium water. In case of pH values of 7.0 or lower add 1 - 2 ml sera pH-minus per 20 liters (5 gal.) of water.