18.02.2016 Why does the pH value in my freshwater aquarium go down? Adding sera KH/pH-plus is recommended to raise the pH value in an easy and efficient way. Photo: © sera The pH value tells the ratio between acids and bases in the water an. Besides the carbonate hardness (KH) is the most important measured parameter in the aquarium. The optimal value depends on the fish being kept. Most ornamental fish species do best at values between 6.0 and 8.5. Values below this limit indicates the water contains more acids than bases. Thre are many possible causes. It basically applies that the lower the carbonate hardness of the water, the fast er the pH value will go down. The KH should therefor be checked regularly, for instance with the aqua test-set by sera. The ideal level is between 5 and 10 °dKH. Roots or peat filters are other factors that can lower the pH value. They enrich the water with organic acids. Adding sera KH/pH-plus is advisable for increasing the pH value in an easy and efficient way. The product precisely and lastingly increases the KH to the desired value. The pH value is gently raised and, above all, safely stabilized as well. It can be corrected to higher levels also by partial water changes with alkaline water.