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Are Wood Tannins Bad For Fish? And Reasons For That

So, you have put driftwood without treating it, and now your aquarium is all black. The discoloration is not a problem, but Are wood tannins bad for fish?

Wood tannins are not bad for fish, depending on the water chemistry and the type of wood. For some fish that prefer lower pH levels, tannins can be great. But, tannins can be harmful to fish that require stable pH levels.

Are Wood Tannins Bad For Fish

What is a tannin?

Tannins are natural polyphenols that occur in many plant species. They bind to proteins and precipitate them out of solution.

Proteins bound by tannins can be precipitated (solidified) along with the tannin molecule itself to form an aggregate with a gelatinous appearance. Tannins can cause water to become cloudy and appear tea-stained.

What types of wood contain tannins?

Oak and other broadleaf trees such as alder, beech, chestnut, willow, hornbeam, birch, etc., are known to have tannins in their heartwood, whereas the sapwood contains fewer tannins.

Maple, Manzanita, and Malaysian driftwood are known to have fewer tannins. Technically it is impossible to find a wood that doesn’t contain tannin because tannin is the compound that gives the plants protection from predators like pests.

How do aquariums get tannins?

Usually, driftwood releases tannins into the water when you introduce them into your aquarium without treating it.

This is the primary way that tannins are introduced into the aquarium. However, some aquarium chemicals also contain tannic acid as an ingredient to change the pH levels of the aquarium. But, they do not release as much tannic acid as driftwood.

How do tannins affect the aquarium?

There are two ways that tannins affect the aquarium.

  • It changes the watercolor – When driftwood leeches tannins into the water, the color changes into a yellowish-brown appearance. This color will not go away for a long time even if you change the water regularly as the driftwood continues to leech tannins until it is all consumed.
  • It changes the pH levels of the water – Tannins initially reduce the pH levels of the water, making it more acidic. This low pH level is beneficial for fish that prefer lower pH levels, like Discus fish and Gouramis. However, this low pH level also causes driftwood’s “phenolic” compounds to begin dissolving, which leech heavy metals into the water. This can be harmful to other fish.

How long do tannins stay in the aquarium?

Tannins will stay in the aquarium as long as the driftwood piece leech out tannins.

When the driftwood no longer has tannins in it, it will stop leeching tannins, and the remaining tannins will go away after about 30 days.

If you have a larger piece of driftwood that leeches more tannins, it will take a much longer time. However, if you choose driftwood with fewer tannins, it will go away much faster.

How long does it take for tannins to leech into the water?

It takes about four days for tannins to leech out into the aquarium water after it has been introduced into your aquarium.

Are wood tannins bad for fish?

Wood tannins are not bad for fish if the fish can adjust and survive.

In fact, many aquarium fish prefer some tannins in the water as they feel much safer in a darker environment.

But, if you need your aquarium water to be stable, then tannins can be harmful as it changes the water properties.

It is advisable to treat driftwood before placing it into your aquarium, especially with a large piece of driftwood that might take a long time before it leeches all the tannins.

Are tannins bad for shrimp?

Tannins are actually good for shrimps as they have antibacterial and antifungal properties that can help with shrimps’ health.

However, if the tannins in the water are too high, they will stain and cloud up your aquarium water. If the tannins are not bad enough to cloud up your aquarium, it is beneficial for shrimps to have some tannins in the water.

However, you should still try to avoid using driftwood with too much tannin content, as it will make your aquarium water darker.

Are tannins bad for goldfish?

Tannins do not harm goldfish, but goldfish are not used to blackwater conditions naturally.

Goldfish inhabit coldwater lakes and ponds filled with lots of algae, and the water in their habitats is more greenish.

So, these fish prefer to live in very clean water with a pH level of around 8.0 to 9.5, but when you introduce driftwood in the aquarium, it will make the water more acidic.

The goldfish will adapt to the new water conditions but, it is always better not to make these significant changes in something your fish are not used to. So, if you have a high tannin driftwood piece, we advise you to first treat it before adding it to your aquarium.

Are tannins bad for bettas?

Tannins are great for bettas because they live in blackwater conditions in the wild. Bettas inhabit shallow, slow-flowing water, often shaded by leaves and other plants.

Therefore, adding driftwood or any other type of wood to the aquarium should be great for bettas.

You can scrub the driftwood to remove dirt before you add it to your aquarium if you want to, but it is not really necessary. Driftwood will be a great choice if you plan to add some tannins to your betta fish tank.

Are tannins bad for guppies?

According to a study, tannins are actually good for guppies and increase their reproduction.

As tannins contain antioxidants and antibacterial properties, they can help with the overall health of guppy fish.

Therefore, it is advisable to include tannins in the aquarium, especially for guppies that live together. But, beware that too much tannin can change the water’s pH level, which might harm your guppies.

Fish that like tannins

Usually, fish that live in blackwater conditions like tannins in their surroundings. Tannin is the component that changes the watercolor and creates a darker environment for these fish. The following are fish that like tannins:

  • Tetras
  • Kuhli
  • Loach
  • Gouramis
  • Cichlids
  • Catfish
  • Guppies
  • Bettas
  • Silver dollars
  • Pacus
  • Shrimps

Tropical fish that need acidic water will also appreciate tannin in the aquarium. Fish with high PH and KH levels will not prefer tannins in their aquarium.

Does all driftwood release tannins?

Yes. Driftwood is a natural source that releases tannins. If the driftwood has been soaked in water for months, then it means that some tannins were already released.

So, if you are lucky to have driftwood that has been in the water for months, it most likely will not release any more tannins into the water.

Does boiling driftwood remove tannins?

Yes. Boiling driftwood is the most efficient way to remove tannins from driftwood.

You can put the driftwood in a pot filled with water, bring it to a boil and let it simmer for about 2 to 3 hours. After that, leave it to cool down before adding the driftwood to the aquarium.

However, you may have to repeat this process a few times before adding it to the aquarium, as some driftwood contains ridiculous amounts of tannin.

Still, some driftwood pieces continue to leach tannins after you boiled them for hours. So, if you have such driftwood, you may have to opt for other methods to remove tannin in the aquarium.

How do you remove wood tannins from an aquarium?

If boiling the wood for a few days doesn’t remove tannins and the wood still leeches tannins into your aquarium, you have several ways to remove these wood tannins from your aquarium.

  1. Change the water regularly

This may seem like a lot of work, but it is one of the efficient methods to remove wood tannins from the water.

As tannins tend to change the pH level of the tank, you will have to remove discolored water to keep the natural chemistry of your aquarium on track.

  1. Add an activated carbon filter

An activated carbon filter is pretty efficient in removing tannins and other impurities from the water. It will stop your fish from getting sick and increase the overall health of your fish.

So, you should consider adding this type of filter to your aquarium, especially if it is heavily populated or has tannin-rich driftwood.

  1. Remove the dead leaves, driftwood, and other organic materials

Dead leaves and other organic materials are other sources of tannins that usually leach into the water. You should regularly remove dead leaves from your aquarium to ensure they won’t increase tannins in the tank.

If you don’t like the discoloration of the water, the best way to get rid of tannins is to remove the driftwood piece from the aquarium.

This will make your aquarium empty, but you can always replace it with an artificial decoration that looks like driftwood.

How long does it take for tannins to go away?

If you don’t do regular water changes, do not have an active carbon filter, and have removed everything that leeches tannins to your water, it will take around one month for the tannins to go away.

But, if you change the water and have an active carbon filter, tannins will go away within a few days.

If you keep the driftwood in your aquarium and expect to have a clean water tank, you will have to wait for months or even years until the wood stops leaching tannins.

If you have a fish tank with lots of water changes, an activated carbon filter, and other efficient methods to deal with the wood tannins, tannin will stop leaching within a few months.

Does water softener remove tannins?

No. You can add a water softener if you have problems related to the hardness of the water, but it will not remove tannins from your aquarium.

Water softeners will only change the hardness of the water, but tannins are organic materials that chemicals cannot remove.

Does a carbon filter remove tannins?

Yes, but it depends on the number of tannins.

If there is not much tannin in the water, an activated carbon filter will remove most of it, but if there’s a lot of tannin in your aquarium, you may need to change the filter not just to remove tannin but also to keep the filter alive.


Wood tannins can be a great addition to your aquarium if you have the right water chemistry and know what type of fish you want.

But, for those who need stable pH levels in their tanks, wood tannins may not be helpful. You must know whether or not the wood is safe for your specific tank before adding it as decoration. 

Credit to : Prime Time Aquatics
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About Dr.Chamika

Hello, I'm Dr. Chamika. I am a Researcher in Water quality, Aquatic organisms, and Environmental chemistry. I am a passionate fish keeper, with10 years of experience. My mission is to help other aquarists experience the joy of fish keeping.