Preparing Driftwood for the Aquarium: Sinking, Tannins and Biofilm
Why new wood floats and stains the water, how to sink it and reduce tannins, and what to do about the white biofilm on fresh wood.
Why new wood floats and stains
Practical Fishkeeping notes that all woods are buoyant and need soaking before use, and that bogwood and Mopani are notorious for leaching tannic acid, which tints the water brown. Tannin Aquatics adds that wood keeps releasing tannins for as long as it is submerged: mangrove tends to release a lot over a long period, while spider wood dumps most of its tannins in a big early burst.
Getting it to sink
Soak a floating piece in a separate container until it waterlogs and sinks; this also leaches out excess tannins at the same time. Depending on the piece, Practical Fishkeeping notes this can take anywhere from a few days to several weeks — dense pieces take longest.
Reducing tannins
- Soak the wood in a bin or bucket, changing the water every few days until it runs clear.
- For a small piece, you can leave it in the tank during cycling (lights off, filter on, about 3-4 weeks) with regular water changes.
- Tough woods such as Malayan driftwood can be boiled to speed up tannin release, though boiling can soften the wood's structure, so many aquarists skip it.
The white biofilm and fungus
A white, slimy fungus or biofilm very often blooms on fresh wood. Practical Fishkeeping explains it feeds on the tannins and sap released by the newly submerged wood; Tannin Aquatics describes new wood as full of bound-up organics that act as 'algae fuel'. It is harmless and normally clears within a few weeks in a well-filtered, cycled tank. Manzanita, spider wood and mangrove are especially prone to it.
Sources: Practical Fishkeeping, What you need to know about tank decoration (www.practicalfishkeeping.co.uk); Tannin Aquatics, The Tint — 'The wood part of the natural aquarium equation' and biofilm tag (tanninaquatics.com tanninaquatics.com).