The Simple Guide to Tannins & Blackwater Shrimp Tanks

A Red Cherry shrimp tank with tannin coloured water

A blackwater tank is simply an aquarium with tannins dissolved in the water. The tannins make the water a dark orangey-brown tea colour.

The dark water is also known as tannic acid. It's a fairly weak acid, and can lower your pH level to somewhere around 6 if you've got a low buffering capacity.

Tannins are harmless, and totally optional. You don't need them in your tank.

If you're only wanting to lower your pH, there are a few other options, like using an active substrate.

Tannins in nature

In the wild, Caridina shrimp live in streams and rivers. Leaves from nearby trees fall into the water and sometimes leech tannic acid.

The leaf litter is also a great source of biofilm, normally making up the bulk of what a shrimp eats in a day.

Making your shrimp tank into a blackwater tank will give them a close match to their natural environment. Keeping your shrimp happy will encourage breeding and boost your colony size.

Benefits of blackwater

Adding tannins into your aquarium has a few benefits:

  • Lowers the pH
  • Can reduce algae growth
  • Helps prevent infections

Tannins lower the pH level

Tannins dissolve in water to create tannic acid. Tannic acid is only slightly acidic, so don't expect a huge change in your pH.

Water with a high carbonate hardness will hardly be affected. Soft water, with around 0-1 KH, will have a more noticeable drop.

Be careful with changing your water parameters as shrimp, Bee shrimp in particular, are very sensitive to parameter swings.

Gradually increase the tannins in your water over a few days or weeks to prevent stressing your shrimp.

Blackwater can slow down algae

The darker water obviously means that less light gets into the tank. In some cases this can slow down growth of both your plants and algae.

Don't expect miracles with blackwater, though. It's only a small change.

It can be helpful when used with other techniques to cut back on algae.

Tannic acid has antibacterial properties

A study found that tannic acid can quickly break down some bacteria, and slow its growth.

This is obviously not a bulletproof way to stop any infections, but it can reduce the risk for your shrimp.

Tannins do not soften water

It's a common myth that adding botanicals like alder cones will soften your water. Unfortunately, it's not true.

An Amano shrimp near some alder cones

You'll get the most effect from tannins in soft water, though.

Hard water with a high KH will buffer away most of the pH change.

How to make a blackwater tank

Making a blackwater tank is fairly easy, you just need to add hardscape or botanicals that release tannins.

You can use any of these in your tank to introduce tannins:

You should prepare your leaf litter by boiling for a few minutes, to prevent the risk of infection.

The longer you boil it, the more tannins you extract, and the less they'll leech in your tank.

Making tannin tea

Don't have much room for wood? Boil the botanicals in old tank water and create a blackwater tea instead.

Keep an eye on the water colour for a few minutes, until it gets to a colour you like.

Once it's cooled down, you can slowly add the tea into your tank and get the perfect strength and colour you're after.

If your water has a high KH level, don't expect much pH movement. You might only get darker water without increasing the acidity much.

How to remove tannins

Changed your mind? Don't like the look of your blackwater tank any more?

Tannins can take quite a while to remove from the water. If you do it too quickly, you could change your parameters too fast and stress your shrimp.

You have a few options to safely reduce tannins:

Chemical and filtration options, like Seachem Purigen and activated carbon, work by absorbing and trapping the tannins.

Performing water changes will gradually make your water clear again. But it can be quite slow if you stick to the rule of not changing more than 20% every two weeks.

Combining water changes with activated charcoal in your filter will be the best way to get rid of your yellow water quickly.

Conclusion

Blackwater tanks are an easy way to make a natural looking shrimp tank.

The tannic acid is totally harmless, and can even help prevent infections.

The tannins in the water can also lower your pH, which is great for keeping your Bee shrimp happy.