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Tannins in the aquarium- The advantages of blackwater

tannins in the aquarium 1

The advantages of Tannins in the aquarium – the blackwater effect.

Tannins in the aquarium

The term Tannins refers to Tannic acid, which often enters the aquarium via driftwood or decorative leaves. Tannic acid, as scary as it sounds is good for most aquariums. All too often I see posts where people are panicking about their water turning brown or yellow after adding wood. But fear not, as it won’t do any harm and if you don’t like the colour then it is easy to fix.

Tannic acid is a natural substance and leaches from new wood or leaves after they are added to the aquarium. This happens in nature too and is often why many freshwater rivers appear to be a brown/yellow colour.

The tea-stained colour that tannins produce is often referred to as the ‘blackwater effect’.

Many aquarists purposely renew aquarium wood or regularly add tannin filled leaves in order to keep their water this way. Many tropical fish originate from blackwater environments so adding tannins to create a blackwater effect on your tank makes the environment more natural for them.


Tannins in the aquarium



Aside from the natural look that tannins produce in your water. It has some effects on your water parameters too. Tannic acid is, unsurprisingly, acidic, so it can lower your pH.

The pH change is usually subtle but you may need to keep an eye on it initially after adding new wood/leaves. If the pH changes too quickly it can cause pH shock in your fish.

Tannins also soften the water. This can be handy if you’re in a hard water area. Many fish, such as tetra prefer soft water, so softening the water naturally is great for them.



How is this a benefit?

Most tropical fish originate in bodies of water that are neutral to slightly acidic. Tannins in the water help to recreate their natural water source, which is where they have spent thousands of years thriving. So putting tannins in the aquarium is great for them.

South American water sources for example are often slightly acidic, between a pH of 5 and 7. Many of these waters are soft too. So if you keep south American fish, adding wood containing lots of tannins to your aquarium can make it very easy to replicate their natural environment.

This all goes out of the window though id you keep fish that do not like these conditions. African lake cichlids for example come from Alkaline conditions and will not appreciate acidic water. Many livebearer species come from hard water sources and do not like softer water.

So, if you keep fish that would suffer from these kinds of changes then the benefits are redundant and you should avoid adding tannins to your tank.



What if I don’t like the look?

It is a frequent sight online to see people asking how to remove tannins from the water. Often this is because they are unaware of any benefits and think something has gone horribly wrong. Sometimes though, it is just an unwanted colour as many people prefer the look of a crystal clear aquarium.

So, if you have added some wood recently and hate the murky brown colouration that has been produced in your water, add some Seachem Purigen. 

Purigen will absorb the tannins in the aquarium and will remove them from the water overnight. Tannins will continue to leach from most woods for a while though, so keep the Purigen in your filter until you’re confident that it has run out.


seachem purigen


Activated carbon can absorb tannins in the aquarium too, but I’ve found it to be significantly less effective. Alternatively, all you need is patience. Over time the wood will cease to release tannins into the water and it will return to the clear water you had before.



Here’s a quick video from Mr Brightfryed on the advantages of Tannins in the aquarium:



Here’s the link to Mr Brightfryed’s channel: Click here!

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Here’s his description for the video:

Benefits to Tannins in YOUR Aquarium | What are Tannins in an Aquarium |

MR BRIGHTFRYED Today I want to talk about the benefits of tannins in an aquarium. It appears the perception of tannins or “TEA” coloured water generally causes a lot of concern for many hobbyists and beginners and will often freak out or franticly ask for help to rid their aquarium of this issue.

In this video, I want to talk about why you might want to consider keeping the tannins and not trying to eradicate them. We go over what are tannins in an aquarium and all the benefits that come with them.



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Frequently asked questions:

Why has my aquarium turned brown?

Aquarium wood, and other botanicals, release Tannic acid into the aquarium. Tannic acid, or Tannins, are yellow/brown in colour and can tint the water.

How can I remove Tannins?

Tannins do have some advantages, but if you don't like the look they provide then they can be removed. Carbon can absorb Tannins but Seachem Purigen works best. Keep a bag of Purigen in your filter until the wood stops leaching the Tannins.


About the author

James @Seriously Fishy

I am a fish keeping enthusiast with over 20 years experience. I currently keep American Cichlids (CA) which are my favourite fish to keep so far. I started Seriously Fishy as I noticed a large volume of people on various web pages looking for help with Aquarium basics. I created the first Seriously Fishy book to solve the issue in 28 pages, that led to the Seriously Fishy UK fish forum and blog.

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  • Tannins cause the brownish or yellowish tint of aquarium water. The discoloration of water is not a significant problem – it will not harm the fish. However, tannins are usually acidic. They will slowly lower the pH of the water, which can ultimately harm the fish.