Driftwood can release tannins for weeks or months, and some pieces continue releasing a smaller amount much longer. The rate depends on wood species, size, age and how much it was soaked before use. Tannins are usually an aesthetic issue rather than a danger, although they can contribute to lower pH in very soft, weakly buffered water. Regular water changes, pre-soaking and fresh activated carbon can reduce visible staining.
There is no universal 'tannin-free after seven days' rule. Two pieces sold under the same trade name can behave differently.
Why duration varies so much
- Different wood species contain different amounts of tannins.
- Thick pieces hold more material than thin branches.
- Previously submerged or aged wood often releases less than very dry new wood.
- Warm soaking water may speed early release.
Brown water is usually not a crisis
Tannins are naturally occurring organic compounds and are intentionally used in some blackwater aquariums. If fish are suitable and water chemistry remains appropriate, the colour itself is not evidence that the water is dirty.
The important distinction is between harmless staining and actual decomposing wood or foul water.
How to reduce tannin colour
- Pre-soak the wood before installation.
- Perform normal partial water changes.
- Use fresh activated carbon if clearer water is a priority.
- Rinse or change pre-soak water until staining slows.
Watch pH in very soft water
In low-KH water, acids associated with botanicals and wood can contribute to a lower pH. In well-buffered water, the effect is often much smaller.
Measure rather than assuming the colour tells you the pH.
Do not keep replacing water just for colour
Large repeated water changes can create more instability than the tannins themselves. If livestock is healthy and parameters are suitable, normal maintenance plus patience is usually enough.
Related aquarium tools and guides
Frequently asked questions
Will tannins eventually stop?
They usually diminish substantially, but some wood can continue releasing a small amount for a long time.
Does boiling remove tannins?
Hot water can accelerate release from small pieces, but it does not guarantee all tannins are removed.
Do tannins lower pH?
They can contribute to acidity, especially in low-KH water, but the effect depends on buffering.
Sources and further reading
This guide separates general aquarium arithmetic from fish-welfare decisions. For species-specific limits, always check the needs of the fish you intend to keep.