How to Remove Tannin from Aquarium Water?

Not all fish come from clear, undiluted water. Some thrive in brackish, discolored water.

The discoloration results from the amount of tannin in aquarium water.

And while it benefits some fish, others do better without it.

It’s also unsightly, which is why some aquarium hobbyists try to reduce tannin levels in their aquarium water. 

How to Remove Tannin from Aquarium Water

One of the most effective ways to remove tannin from aquarium water is by using activated carbon.

Activated carbon is carbon composed of:

  • Charcoal granules
  • Heat 

It’s also been altered on a chemical level to make it more absorbent. This helps bind tannins together and remove them from the water.   

However, it’s not necessary to add the activated carbon to the water directly. A good quality aquarium filter contains it and will remove the tannin within hours. 

One thing you should keep in mind is that no filter lasts forever. If you find your aquarium has routinely high tannins, it may be time to replace the filter. 

Alternatively, you may want to consider another water source.

Reasons to Remove Tannin from Aquarium Water

Of course, how much tannin you need to remove depends on the water you fill your aquarium with. 

Tannins naturally soften water, and that affects the pH and alkalinity of your fish’s environment. Depending on their natural habitat, that may not be a good thing. 

Where Tannins Come From 

You’re also much more likely to see tannins in water that traverses marshy or that overlaps areas of plant and animal decay. 

This is because tannins are naturally occurring in organic matter. 

Alternative Ways to Remove Tannins from Aquarium Water

Tannins are also challenging to remove completely.

In addition to filtration systems, here are some of the most efficient ways of removing tannin from your aquarium water.

Distilled Water

The first method is to soften hard water by filling your aquarium with equal parts tap water and distilled water

Distilled water breaks down naturally occurring compounds and chemicals in the water. That means that by mixing it with tap water, you significantly reduce the tannin in your aquarium. 

Add Rain Water to Your Aquarium Environment

Another way to lower the tannin levels in your aquarium is by mixing your tap water with or substituting rainwater. 

Rainwater is naturally softer than most tap water. However, it’s also more acidic because it is partially composed of dissolved carbon dioxide. 

Consequently, collecting rainwater for your aquarium isn’t as simple as sticking a tub under the nearest eaves trough or drain pipe. 

Before you collect rainwater for your aquarium, ensure:

  • The drainpipe isn’t metal
  • The drainpipe is clean
  • Run-off area is low in atmospheric pollution

Another trick when collecting rainwater is to give the rain a few minutes to clean out the interior of the drain pipe you’re collecting rainwater from. 

This reduces the likelihood of extra detritus accruing in the water. 

One important thing to note is that because rainwater bypasses the organic material that generates tannins, it has a lower tannin level than tap water in certain areas. 

Ion Exchange 

Usually, ion exchange is described as a water softening process. But it’s also effective as a way to remove tannins from aquarium water. 

Ion exchange works by triggering a chemical reaction between ions. In it, the ions under exchange get replaced by similarly charged ions with different properties. 

So, because tannins are negatively charged, they are treated with anion resins. The anions attract the negative tannin ions and replace them with similarly negative ions. 

However, these do not possess the tannins or attendant water-softening properties. 

An additional benefit of anion resin treatments for aquarium water is that it only removes tannins. This is useful because your fish need certain minerals to survive. 

However, there’s a chance that anion resins can chemically alter your aquarium water’s pH or chloride levels. 

Consequently, you’ll want to monitor the composition of your aquarium water to ensure it’s comfortable for the fish.  

Reverse Osmosis 

Another way to lower the tannin in your aquarium is by fixing a reverse osmosis filter to your tap. 

In traditional osmosis, molecules diffuse equally across a semipermeable membrane. Reverse osmosis alters the process, ensuring only pure water molecules pass the membrane.  

This means that any additive compounds in your tap water, like tannin, get filtered out. The water is consequently softer and clearer to look at. 

Baking Soda 

Any tea granny will tell you that if you want to effectively de-tannin your teapot, you rinse it with baking soda. And you can do the same thing with water.

Add one tablespoon of baking soda to every five gallons of water, and you’ll be set. However, baking soda also raises the pH level of the aquarium water.

Just as different fish thrive on different tannin levels, they also have different pH needs from their water. So if you do decide to use baking soda, do your research first. 

Find out how to test the pH of your aquarium’s water and what level the fish swimming in it need for the tank to be habitable. 

Remember, if you decide to use baking soda to lower the tannin levels, you remove the fish from the tank first. 

Suddenly lowering the pH level of their water with the fish present can adversely affect them. 

Be Mindful of What Goes Into the Aquarium 

All aquarium hobbyists enjoy embellishing their fish’s habitat with decorations. But not all decorations are created equal. 

This is important if you are trying to recreate a particular fish’s habitat or want to reduce the amount of tannin in the water. 

In particular, driftwood releases natural tannins into the water. So, while driftwood logs might look elegant, they’re to be avoided if you want clearer, softer aquarium water. 

To ensure you don’t unwittingly increase the tannin levels in your aquarium water, avoid adding:

  • Driftwood
  • Peat 
  • Indian almond leaves
  • Oak leaves 

When You Need Tannins in Your Aquarium Water

While it’s understandable to want to remove tannins from your aquarium, sometimes they’re necessary. 

Various fish come from blackwater or tannin-enriched water. If this is true of your fish, then removing tannins from their water supply may do more harm than good. 

That makes it vital that you only remove tannins deliberately and when necessary instead of purely for aesthetic reasons. 

For instance, fish native to the Amazon and Congo regions are most colorful when their habitat contains tannins. This is true of:

Still, other fish find tannin-heavy water an impetus for breeding.

So, depending on the fish, it may be worth forgoing the filter if you’re hoping to raise more of a particular fish.


Tannin in tank water has its advantages, but not everyone appreciates the color. And not all fish need brackish, tannin-rich water to flourish.  

That being the case, there are a variety of ways to remove tannin from your aquarium water, some more time-consuming than others. 

Whatever method you choose, keep an eye on the pH of the aquarium water to avoid shocking the fish with a sudden drop in acidity or increased alkalinity. 

Finally, avoid plants prone to releasing tannin, and the result should be a clear, aesthetically pleasing aquarium. 

Other articles you may also like: