Driftwood & PH Levels

Aquarium driftwood adds natural elegance to freshwater aquariums, but many enthusiasts are concerned about long-term impacts on the tank's pH levels. While driftwood does, in fact, have an effect on water chemistry, several other factors need to be considered to understand the prolonged changes that natural wood can cause in aquariums.

  1. Tannins and pH

    • Driftwood, like almost all tree and plant matter, contains tannic acid, a natural compound which acts to protect the wood from fungus and disease. Tannic acid is the product in driftwood which gives the water a tea-colored stain, and also the compound which acts to lower the pH of aquarium water. While this drop in pH is generally not significant in most tanks, if a large amount of driftwood is clustered into a relatively small gallon-size tank or bowl, a drop of up to a point or two might be detected on pH testers.

    Buffering Capacity

    • The relative carbonate hardness of water is measured as KH. KH essentially measures the buffering capacity of the water, or the water's ability to stabilize when faced with the introduction of foreign elements such as chemicals or new water. Higher KH is, largely, a good thing--it provides more of a cushion against pH or nitrite swings, and helps the pH stabilize after a change. But depending on the KH level of the tank in question, the pH may actually balance out to right where it was before driftwood was added. Conversely, tanks with low KH may see a more significant temporary drop in pH when driftwood is added.

    Water Changes

    • Since the driftwood can only affect the pH of water it is directly exposed to, large water changes may cause the tank pH to swing up and down. Care should therefore always be taken when undergoing water changes in a tank with a large amount of driftwood, as abrupt changes in pH can be very hard on fish. Frequent, small water changes are generally a safe way to avoid this dilemma.

    Long-Term Effects

    • As mentioned, tannic acid will leach from driftwood in greatest quantities when it is first added to the aquarium. Changes in pH also will be most noticeable in the first few months after new wood is added to the tank. Over time, as the tannins in the wood dissipate, the pH will slowly stabilize and return to just under the normal level.

    Soaking and Boiling

    • To eliminate most of the problems associated with pH swings in the tank due to driftwood, any new wood can be boiled and soaked in hot water to help draw out some of the tannic acid. Boiling can be done in a large soup or lobster pot, and bigger pieces of wood can be soaked in a bathtub full of hot water. Frequent water changes will help as tannic acid is extracted from the wood.