How to Get the Alkalinity Up in an Aquarium

In aquarium water chemistry, alkalinity describes the ability of the water to resist changes to its pH level -- a measurement of acidity. The scale runs from zero to 14, with 7 being neutral. Numbers lower than 7 are acidic, while numbers higher than 7 are basic. Every species of fish thrives within a certain pH range. Generally, most species are tolerant of pH values in the 6 to 10 range. Water that becomes too acidic will sicken or kill fish, so keeping the alkalinity of the tank high is essential.

Things You'll Need

  • pH test strips
  • Oyster shell, coral gravel or dolomitic limestone
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Instructions

    • 1

      Monitor the pH of your aquarium's water, using a test strip as directed on the label. A reading of 4 or below indicates that the alkalinity the water has dropped, leading to a buildup of acid. This is the danger zone for the health of your fish.

    • 2

      Replace a portion of the water with filtered water of the same temperature, if the level is 4 or below. This will improve the pH level somewhat while you work to increase the water's alkalinity.

    • 3

      Add oyster shell, coral gravel or dolomitic limestone to the tank, to raise the alkalinity. These substances leach carbonate ions that buffer the water against sudden drops in pH level.