White Biofilm on New Driftwood: Harmless and Temporary

The fuzzy white film on fresh driftwood looks alarming but is a harmless, temporary biofilm. Learn what it is and how to handle it.

A few days after adding new driftwood to a tank, many aquarists find it coated in a slimy white or grey fuzz that looks like mold or fungus. It is one of the most common scares for newcomers, but in almost every case it is a harmless, self-limiting biofilm rather than anything dangerous to fish or plants.

What it is

When an organic object such as driftwood is placed underwater, it tends to grow a layer of biofilm made of harmless bacteria and other microorganisms. A biofilm is a community of microbes, including bacteria and fungi, living in a self-produced slimy matrix on a surface. On fresh wood this growth is fed by sugars and other organic compounds leaching out of the new, uncured timber, which is why it is heaviest on recently added driftwood and on softer woods. The very same harmless growth often appears as white mold, fluffy fungus or short tufts of grey hair on new plant bulbs, and it is not dangerous to the plant and does not spread to other plants.

Why it is temporary

The bloom is driven by the easily-available nutrients leaching from new wood. As those surface compounds are used up and the tank matures, the food supply dwindles and the biofilm naturally recedes, typically over a few weeks. Meanwhile, grazing animals treat it as food: if you have algae eaters, shrimp or snails, they will often consume this fuzzy layer for you, clearing the wood faster than you could by hand.

What to do

• Do nothing: in most tanks it self-resolves as the wood is depleted and a clean-up crew grazes it.
• Let grazers help: shrimp, snails, otocinclus and many other fish readily eat the biofilm.
• Remove it manually if it bothers you: siphon it off during a water change or gently brush the wood.
• Pre-soak, cure or boil new wood before use to leach out organics and reduce the initial bloom.
• Maintain good water flow across the wood, since stagnant areas let films build up more.