A common sight in newly set up aquariums is the appearance of a white, often cotton-like growth covering submerged driftwood. While visually unappealing, this temporary bloom is a frequent and normal occurrence when introducing fresh wood. It is generally not a threat to healthy aquatic inhabitants or the stability of the tank itself. This growth indicates the wood has begun releasing organic compounds into the water.
Understanding the Fungal Growth
The white substance observed on new driftwood is a type of biofilm, a complex colony of microorganisms like bacteria, yeasts, and molds that adhere to a surface. This growth is often identified as a water mold, or oomycete, frequently belonging to the genus Saprolegnia. Although commonly called a fungus, Saprolegnia is technically classified as a protist, related more closely to algae than to true fungi.
This growth is triggered by the leaching of excess organic compounds from the wood after submerging. New driftwood contains residual sugars, proteins, and other organic matter. As the wood absorbs moisture, these compounds are released, acting as a readily available food source. Dormant spores and bacteria already present in the water rapidly colonize the surface, and the growth continues as long as these nutrients leach from the wood.
The appearance of this biofilm is distinct from persistent molds that might indicate decay or poor water quality. It typically has a slimy or cottony texture and is localized to the new wood. The growth is opportunistic, feeding solely on the nutrient-rich compounds being released, and it will naturally recede once this food source is exhausted.
Immediate Removal Techniques
For those who find the white growth unsightly, mechanical removal offers the most immediate solution. The wood can be scrubbed clean with a dedicated toothbrush or a soft brush while it remains in the aquarium. Gently scrubbing the affected areas dislodges the biofilm from the wood’s surface.
Immediately following the scrubbing, the dislodged debris should be removed from the water column to prevent it from settling elsewhere. This is best accomplished by using a siphon or a gravel vacuum to suck the floating particles out during a routine partial water change. If the wood is small enough, removing it entirely for a thorough scrub under running water and a rinse can be a more effective way to ensure all residue is removed.
A biological approach uses certain aquarium inhabitants to consume the biofilm, effectively acting as a cleanup crew. Various snails, such as Nerite snails, and certain types of shrimp, particularly Amano shrimp, will readily graze on the white film. Plecostomus and Ottocinclus catfish are also known to help clean the surface of new wood. Introducing these grazers can manage the growth without the need for manual intervention.
Even without active removal, the growth is self-limiting and will typically disappear on its own. The microorganisms consume the available sugars and proteins within a period that usually ranges from a few weeks to a couple of months. While waiting for this natural process to conclude, ensuring good water flow around the wood helps prevent the biofilm from becoming excessively thick.
Preventing Recurrence and Future Growth
The most effective way to prevent the initial outbreak is to properly prepare the driftwood before introduction. Pre-boiling the wood is an excellent method, as the sustained, high temperature serves multiple purposes. Boiling rapidly sterilizes the wood, killing existing surface spores, and significantly accelerates the leaching of organic compounds that feed the biofilm. Repeating the boiling process, changing the water each time until it remains relatively clear, can drastically reduce the chance of growth.
Extended soaking, or curing, is another method, especially for pieces too large to boil. Submerging the driftwood in clean water for several weeks allows the water-soluble compounds to leach out slowly. The soaking water should be changed every few days to remove accumulated organics, preventing the biofilm from establishing in the container. Curing also ensures the wood becomes completely saturated, which helps it sink immediately and stabilizes its structure.
Maintaining excellent water quality once the wood is introduced further discourages any minor recurrence of growth. Regular partial water changes reduce the concentration of free-floating organic nutrients that may have leached into the tank. Using chemical filtration media, such as activated carbon or specialized resins, can absorb dissolved organic compounds. This effectively removes the food source for the biofilm organisms, contributing to a cleaner aquatic environment.