How Does Tannic Acid Affect Aquariums?

When you added a piece of driftwood to your fish̵7;s home to beautify the aquarium, did it change the water's color? A darkened shade or murky brown tinge is the effect of tannic acids, or tannins, that leached out from the driftwood.

  1. Tannic Acid

    • Tannins are acids that leach out of some types of wood when it soaks in water. While tannins will turn a body of water the color of tea, they are not dangerous to fish. Malaysian driftwood has the most tannins, with Mopani or African driftwood coming in second. American driftwood has the fewest tannins, according to FishChannel.com.

    Color Change

    • The most noticeable effect of tannic acid is that it will turn the color of the water yellowish-brown. This can simulate the black water of the amazon, mimicking the natural habitat of some tetras. To clarify the water in your aquarium, add a carbon filter and perform weekly water changes. These measures will reduce water discoloration. It can take several weeks to reduce the discoloration.

    Acidity Change

    • Since tannins are acids, they will lower the water pH, making it more acidic. This can be good for some species of fish. But if your fish prefers more alkaline water, like cichlids, it could be harmful if the pH becomes too low. Adding coral can raise the pH and counteract the effect of the tannins. Test your aquarium̵7;s pH if you add driftwood to make sure it is not too acidic for your fish. In most cases, the change to water chemistry is minor and will not affect your fish.

    Reducing Tannins

    • If you simply want your wood to look pretty and not change the color or pH of your aquarium̵7;s water, you can treat driftwood to reduce tannin leaching. Soaking driftwood in clean, chlorine-free water will allow the tannins to leach out prior to adding them to your tank. It̵7;s best to soak for a week or two, changing the water frequently as it becomes dark. Soaking has the added benefit of reducing driftwood̵7;s buoyancy, making it sink easier. If a one- to two-week soak isn̵7;t quick enough for you, boil the driftwood for a couple of hours to accelerate the leaching of tannins. Boiling also sterilizes the wood, killing any fungi or bacteria that may be present.