Everything about wood in the aquarium

Frequently Asked Questions About Roots

• Is the root of a coniferous tree suitable for an aquarium?
• Is the fruit tree root suitable for an aquarium?
• Does the root purchased from a pet shop need to be prepared?
• When will my root start to sink?
• Does brown water harm fish?

These and other questions trouble many, less or more experienced, aquarists. Since there are many myths and false information regarding both the properties of the tree itself, its toxicity, usefulness or possible use in our tanks, in this article, I will try to bring this topic closer to our readers.

Types of wood

Let's start with types of trees that we would like to use for our aquarium setup:

• deciduous trees - in Poland you can find the following species: oak, beech, birch, ash, alder, hornbeam, poplar, maple, lime, willow, elm;
• fruit trees - these are also deciduous trees belonging to the Rosaceae family, common species in Poland include: Aronia, peach, cherry, pear, apple, rowan, hawthorn, almond, apricot, quince, plum, cherry;
• coniferous trees - in Poland, common species include: pine, spruce, fir, larch and yew.

And how to check if we are dealing with hardwood or coniferous wood? There is a simple method that requires drilling deep holes in an invisible place and smelling the shavings. Conifer wood can be recognized by its resinous smell (turpentine smell), fir additionally emits a vanilla smell, oak wood and black poplar emit a distinctive tannin odor - a tart-acid smell.

Definitions and parameters concerning wood

What else should you know about wood before you decide to prepare it:

• heartwood, non-heartwood/white wood: almost every tree with age (various for each species) produces heartwood, that is, it loses its ability to conduct water in some of its cells. These cells are impregnated with heartwood substances: resins, gums, tannins, dyes, etc. Heartwood always occurs in the oldest part of the tree, its center, and expands outward. The rest of the tree, which conducts water, is called sapwood. The ratio of heartwood to sapwood depends on the species of the tree. There are also a few species in which heartwood does not form at all. These are: birch, beech, hornbeam, sycamore, chestnut, common maple, alder, aspen. Heartwood has a higher density than sapwood.
• chemical composition of wood: each type of tree consists of cellulose, lignin, hemicellulose and additional substances, where the first 3 compounds make up 90-95%. Depending on the type of tree (deciduous, coniferous) the percentage of the main compounds is different. Coniferous trees contain more cellulose and lignin compared to deciduous trees. From the aquarist's point of view, additional substances are important, which are more or less toxic to the inhabitants of our aquariums. These include tannin substances (common in all types of trees) and resins (occurring only in coniferous trees). These substances mainly serve to protect plants in case of their damage as a result of the action of fungi, bacteria or pests. Substances dangerous/toxic to fish include primarily: tannins and other phenolic compounds contained in deciduous wood (tannin substances), cyanogenic glycosides in fruit wood (a type of tannin substance) and resin acids, phenolic acids in coniferous wood (resins). The toxicity of these compounds is primarily based on them getting into the aquatic environment and undergoing transformations that lead to changes in the properties of this environment. Some of them dissolve in water, some do not, some undergo hydrolysis, resulting in new compounds, etc.
• there are also other components dangerous to fish, which trees produce for protection. An example can be taxine (a toxic alkaloid produced by common yew) or sambunigrin (a poisonous glycoside produced by black elder).

It is also worth discussing some parameters of wood, which from the point of view of the aquarist are important. These include:

• Wood absorbency - is the ability of wood to absorb water. This value is strictly dependent on the density of the wood - as the density increases, its ability to absorb water decreases. Low-density wood (hence, lower weight) has more pores/vacant spaces through which water freely flows. This is exactly the type of wood that takes less time to fully absorb - that is, it sinks in a shorter time.

  Type of wood	Density of completely dry wood [kg/m3]
  Hornbeam	830
  Ash	750
  Beech	730
  Oak	710
  Elm	680
  Maple	660
  Birch	650
  Larch	600
  Lime	530
  Alder	530
  Pine	480
  Fir	450
  Poplar	440
  Spruce	430

• wood drying time: the length of this time depends on several parameters: type and thickness of wood, speed of air circulation (the greater the airflow, the faster the wood dries), air humidity and the condition of the wood surface (wood with bark dries much slower). Here, too, wood density influences: high density - longer drying time, as the pores/free spaces are smaller and the air has more difficulty in free circulation.
• durability of wood against factors causing their decay, in this case the action of water and fungi. Contrary to popular belief, the hardness of the wood does not affect its durability, but: age, amount of lignin (the more, the wood is more durable and more resistant to fungal attack), type of wood (heartwood or non-heartwood/white wood - the first one is more durable), ambient temperature (constant is more advantageous), type of environment (saltwater speeds up wood decay). Durability of wood completely submerged in water:

  Type of durability	Wood type
  Very durable	Oak, hornbeam, elm, larch, pine
  Average durability	Beech, alder, fir, spruce
  Not very durable	Birch, maple, ash, chestnut, lime, poplar, willow

  Wood resistance to fungal attacks:

  Type of resistance	Type of wood
  Durable	Oak, black locust
  Average durability	Fir
  Slightly durable	Spruce
  Not durable	Beech, ash, poplar

Wood preparation

There is no tree that would be indifferent to the inhabitants of the aquatic environment. Each type of tree contains some toxic compounds, which are washed out by the influence of water and can be a threat if a certain concentration of this compound is exceeded. The goal of wood preparation is to disinfect the wood, neutralize dangerous compounds to minimize their toxic impact in our aquarium as much as possible. Therefore, this activity is necessary for both purchased roots and those independently searched for.

The method of wood preparation strictly depends on its type: deciduous, coniferous, fruit and whether it is fresh (live), or dried (dead). Roots/pieces of wood/branches that are rotten (at various stages of decomposition) or largely covered with mold/fungi etc. are not suitable for preparation.

Preparation of deciduous wood

The harmful substances for fish in this case are tannins (mainly tannins and phenolic compounds), which need to be minimized as much as possible through proper wood preparation.

Root purchased in a store or fished out of a swamp/peatland/water tank, where it has been for several years:

• mechanical cleaning of the root from bark residues or other impurities, e.g. using a brush, grinder, pressure washer,
• root disinfection - aimed at removing potential fungi, bacteria, and insects. Disinfection is carried out in a water and salt solution (for each liter of water, add 1 tablespoon of salt - there is no need to increase this amount, as salt is only for disinfection, it does not accelerate the removal of tannins from the tree), in a solution of rivanol and water (pill for each 40 liters of water) or a solution of potassium permanganate and water. High temperature effectively kills fungi (they die at 60°C), so we should boil the root for about 30 minutes (there is no need to extend this process, as it doesn't affect the sinking of the root or accelerate the removal of tannins from the tree),
• Boiling wood in water without the addition of a disinfectant – also for about 30 minutes (there is no need to extend this process, as it doesn't affect the sinking of the root or accelerate the removal of tannins from the tree),
• leave the root to cool and thoroughly rinse it in water, which we add to the aquarium e.g. during replacements,
• check whether the root does not release color and whether it sinks - we put it in a container with water (temperature as in the aquarium) for several hours. If the water did not color or only colored slightly, and the root is sinking without any problem, you can safely place it in the aquarium (remembering in the second case the regular 10-20% water exchanges until the coloration disappears). If the root does not sink, it is weighted and we wait for it to soak (become soaked with water). When the root colors the water intensively, we also leave it in a separate tank, changing the water daily with fresh one, and wait until the coloration completely or significantly disappears.

Found dry/dead root from a deciduous tree:

• barking the wood: the bark should easily come off using hands or e.g. a chisel. However, if we have any problems with this operation, we should bark the wood after boiling in water alone (0.5h should be sufficient),
• root disinfection - aimed at removing potential fungi, bacteria, and insects. Disinfection is carried out in a water and salt solution (for each liter of water, add 1 tablespoon of salt - there is no need to increase this amount, as salt is only for disinfection, does not accelerate the removal of tannins from the tree), in a solution of rivanol and water (pill in every 40 l of water) or solution of potassium permanganate and water. High temperature effectively kills fungi (they die at 60°C), so we should boil the root for about 30 min (there is no need to prolong this process, as it neither speeds up the sinking of the root nor accelerates the removal of tannins),
• boiling the wood in just water without a disinfectant - also for about 30 minutes (there is no need to prolong this process, as it neither speeds up the sinking of the root nor accelerates the removal of tannins),
• soaking the wood - to make it saturate and reduce its toxicity (substances dangerous for fish, mainly tannins and phenolic compounds, dissolve in water and there is less and less of them with each exchange of it). The wood needs to be weighted, and we replace the water daily with fresh. The length of soaking the wood depends on the level of its drying, dimensions, and absorbency. You cannot speed up the process,
• rinsing the wood thoroughly in water, which we add to the aquarium e.g. during replacements,
• placing the root in the aquarium.

Fresh/live deciduous wood – such wood has the highest amount of harmful substances:

• leaving the wood in the natural environment (outdoors) or sinking it in a water tank / peatland / swamp to allow the self, natural process of neutralizing the toxicity of this wood by microorganisms, this process should last up to a year (the larger the root the longer), we should interrupt the process in the summer season, after a long period of sunlight, when the tree will be dry/partially dry. We cannot replace the process with express drying in the oven or microwave, unless it is a very small specimen,
• barking the wood, if we have problems with this we can previously boil the wood in just water (about 30 minutes),
• root disinfection - aimed at removing potential fungi, bacteria, and insects. Disinfection is carried out in a water and salt solution (for each liter of water, add 1 tablespoon of salt, there is no need to increase this amount as salt is only for disinfection, does not accelerate the removal of tannins from the tree), in a solution of rivanol and water (pill in every 40 l of water) or solution of potassium permanganate and water. High temperatures effectively kill fungi (they die at 60°C), so we should boil the root for about 30 min (there is no need to prolong this process, as it neither speeds up the sinking of the root nor accelerates the removal of tannins from the tree),
• boiling the wood in just water without a disinfectant - also for about 30 minutes (there is no need to prolong this process, as it neither speeds up the sinking of the root nor accelerates the removal of tannins),
• soaking the wood - to make it saturate and reduce its toxicity (substances dangerous for fish, mainly tannins and phenolic compounds, dissolve in water, and there is less and less of them with each exchange of water). The wood needs to be weighted and we replace the water daily with fresh water. The length of soaking the wood depends on the level of its drying, dimensions, and absorbency. You cannot speed up the process,
• rinsing the wood thoroughly in water, which we add to the aquarium e.g. during replacements,
• placing the root in the aquarium.

Preparing fruit tree wood

The substances harmful to fish in this case are tannins - cyanogenic glycosides, which dissolve perfectly in warm/hot water and are removed with it. Therefore, only large roots require prior seasoning/drying.

Dry/dead root that has been lying outside for several years and small roots/branches alive/fresh:

• barking of wood: in this case, the bark should easily come off using hands or, for example, a chisel. However, if we have any problem with this task, then we should bark the wood after boiling in water alone (0.5h should be enough),
• disinfection of the root - aims to remove potential fungi, bacteria and insects. The disinfection is carried out in a solution of water and salt (for every liter of water we pour 1 tablespoon of salt - there is no need to increase this amount, because salt is only for disinfection, it does not speed up the removal of tannins from the tree), in a solution of rivanol and water (tablet for every 40 liters of water) or a solution of potassium permanganate and water. High temperature effectively kills fungi (they die at 60°C), therefore, we should boil the root for about 30 minutes (there is no need to extend this process because it does not affect the acceleration of sinking the root),
• boiling the wood in water without the addition of a disinfectant - aims to neutralize the disinfectant and also dangerous substances for fish - cyanogenic glycosides. The bath should last about 30 minutes and we should repeat it several times (each time we replace the water with fresh water),
• soaking the tree - to saturate it. The wood should be weighted and remember to change the water for fresh (unfiltered, unaerated will start to spoil). The length of soaking the wood depends on the degree of its drying, dimensions and absorbency. The process cannot be accelerated,
• thorough rinsing of the wood in the water, which we add to the aquarium for example during replacements,
• placing the root in the aquarium.

Large fresh/live roots that we cannot boil:

• leaving the wood in a natural environment, outside or drowning it in a water tank/peat bog/bog to self-neutralize the toxicity of this wood by microorganisms, this process should take several months (the larger the root, the longer),
• barking of wood: in this case, the bark should easily come off using hands or, for example, a chisel. However, if we have any problem with this task, then we should bark the wood after boiling in water alone (0.5h should be enough),
• disinfection of the root - aims to remove potential fungi, bacteria and insects. The disinfection is carried out in a solution of water and salt (for every liter of water we pour 1 tablespoon of salt - there is no need to increase this amount, because salt is only for disinfection, it does not speed up the removal of tannins from the tree), in a solution of rivanol and water (tablet for every 40 liters of water) or a solution of potassium permanganate and water. High temperature effectively kills fungi (they die at 60°C), therefore, we should pour boiling water over the root and soak it for about 30 minutes (there is no need to extend this process, as it does not affect the acceleration of the sinking of the root), the water should always be hot,
• soaking the wood in boiling water (the water should always be hot) without the addition of a disinfectant - aims to neutralize the disinfectant and also dangerous substances for fish - cyanogenic glycosides. The bath should last about 30 minutes and we should repeat it several times (each time we replace the water with fresh water),
• soaking the tree - to saturate it. The wood should be weighted and remember to change the water for fresh (unfiltered, unaerated will start to spoil). The length of soaking the wood depends on the degree of its drying, dimensions and absorbency. The process cannot be accelerated,
• thorough rinsing of the wood in the water, which we add to the aquarium for example during replacements,
• placing the root in the aquarium.

Preparing coniferous wood

In this case, the most harmful compounds for fish are resins (resin acids and their derivatives). The only species that does not have resin ducts and does not produce resin cells is fir. Resins are compounds insoluble in water, so soaking/cooking such wood for a long time to get rid of these compounds makes no sense - their toxicity is still the same. Also, long drying does not completely neutralize resins (only volatile compounds) as they also contain non-volatile compounds (hard to evaporate). Therefore, we prepare dry/dead wood and fresh/live wood in exactly the same way, with the second case the process will take much longer. The preparation of coniferous wood involves neutralizing the resin acids with a solution of sodium hydroxide NaOH (saponification) - the product of the reaction will be sodium resin, well soluble in water. Stages of preparation:

• cleaning the tree from bark - if we have a problem with this task, then we should bark the wood after boiling in water alone (0.5h should be enough),
• saponification of resin acids in a 2-3% aqueous solution of sodium hydroxide (NaOH), the solution should be warm (temperature 40-70°C). As a result of the reaction, soaps are formed (we will recognize their formation by the slippery surface of the wood, foam can form) well soluble in water,
• neutralization of hydrogen peroxide - we rinse the root in warm water with a small addition of hydrochloric acid HCl (1-2% solution), it can be replaced with common citric acid,
• we repeat the cycle of saponifying the resin acids and neutralizing the hydrogen peroxide until the saponification stops,
• the wood at this point should already sink, but if it does not, we soak it in the same way as deciduous wood,
• we thoroughly rinse the wood in the water, which we add to the aquarium for example during replacements,
• placing the root in the aquarium.

Using this method, be extremely careful when contacting chemicals and during the baths themselves - apply personal safety measures (rubber gloves, eye protection, respiratory protection) and carry out the entire process in a well-ventilated room. Preparing the wood with this method is intended for adults and responsible ones.

Theoretically, well-prepared coniferous wood should not pose a risk to our fish. However, in practice it may turn out that the soap-making process was too short, and sodium hydroxide was not completely neutralized. Therefore, every aquarist must decide for himself whether he wants to take the risk associated with it and expose his charges to it.

Additional information

Large roots that do not fit in any cooking vessel are flooded with boiling water (with or without a disinfectant) in a suitable container, for example a bathtub, barrel etc.

Every root, regardless of the type of wood, gradually decomposes in a water environment. As a result of this decomposition, a brown coating forms on the root, which dirties the hands. In suitable and favourable conditions, the wood is also attacked by various species of fungi (mainly mouldy) or bacteria. We should therefore test the water parameters, eliminate the potential cause of mould and clean the root mechanically and by reboiling it (fungi die at a temperature of 60°C).

A poorly prepared root or a rotten/rotting root significantly colours the water, it can cause water spoilage, its unpleasant smell, and fish dying.

We do not varnish the roots - every type of paint is toxic, not to mention that a varnished root will never sink, and a wet root cannot be varnished (the paint will not stick).