Controlling pH for Fish

Most aquarium fish have a specific ideal pH range. Technically, pH is the negative log of the hydronium ion concentration of a given sample of water. All this means is that pH tells you how acidic or basic water is on a scale of 1 to 14, with 7 being neutral, numbers higher than 7 basic, and numbers lower than 7 acidic. Water's pH relates closely to hardness, in that hard water usually has a higher pH than soft water. In the home aquarium, you have several methods to manipulate pH to get it closer to a fish's ideal range.

  1. Do Your Homework

    • Some aquarium fish can adapt to a wider range of pH.

      Always research the needs of your exact fish before changing the pH. Some fish need an acidic pH and some need a more basic pH. And many common, popular aquarium fish can adapt to a range of pH, and will probably do fine in dechlorinated tap water. Most sources that list a fish's preferred pH will also mention its ideal hardness, a closely-related water parameter that measures how much the water resists changes in pH.

    Going Up

    • In the aquarium hobby, the phrase "African cichlids" usually refers to cichlids from the African Great Lakes.

      It is generally easier to raise an aquarium's pH than it is to lower it. You can raise pH by dissolving bicarbonates and calcium in the water. Decorating the aquarium with limestone and coral sands will raise the pH and hardness, since these decorations leach minerals into the water. You can also use products like African cichlid salts, mineral salts sold at pet shops, which buffer aquarium water at a higher pH. This makes the water ideal for fish like African cichlids and Central American livebearers, which prefer hard, alkaline water. These methods will all raise the pH of aquarium water.

    Soften It Up

    • The Rio Negro River takes its name from its dark, acidic water.

      You can soften your aquarium water a number of ways. You can filter your water with a process called reverse osmosis, usually abbreviated RO in the aquarium hobby. This process removes minerals from water, softening it and making it easier to acidify. You can also decorate the aquarium with driftwoods like mopani wood and Malaysian driftwood. These woods absorb minerals and leach organic acids into the water, softening it and lowering the pH.

    A Note of Caution

    • Stress can lead to disease in aquarium fish.

      Keep in mind that fish react very poorly to changes in pH, even changes towards their ideal pH. Never change the pH by more the 0.2 per day in either direction. Greater changes than this stress fish. Stressed fish find themselves less able to fight off disease and are more likely to die. Make changes to the pH slowly and carefully to avoid harming your fish.