The Complete Blackwater Aquarium Guide

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Blackwater aquarium? You may think this doesn’t sound like an attractive aquarium, but you’d be wrong! 

In this article, I’ll explain what a blackwater aquarium is, and how to properly set one up.

What Is A Blackwater Aquarium?

First things first, we need to understand what a blackwater aquarium is. So what is it?

Simply put, a blackwater aquarium is a dark water aquarium that emulates the darker waters of the Amazon.

There are two types of fish tanks, whitewater tanks and blackwater tanks. We generally are more familiar with the whitewater tanks, which have a neutral 7.0 pH and relatively clear waters. Blackwater tanks however, have darker-colored water through large amounts of dissolved humic substances in the water. Often, this is because of leaf litter, decomposing plants and fruit, wood, and similar debris.

Blackwater environments are often called root forests, and tend to house over 200 species of freshwater fish.

Blackwater aquariums don’t literally have black H20 in it, but the water is dark enough that most plants and fish cannot thrive in it. In some cases, fish will be virtually invisible swimming around in the tank, which can be a turn-off to many fishkeepers. But there are many reasons why this type of aquarium does appeal.

For those seeking an interesting challenge, a blackwater aquarium is a good choice. If done correctly, a blackwater aquarium will simulate the natural environment for freshwater fish and other critters. For many hobbyists, this challenge is a fun way to dig deeper into fishkeeping without having to blow the bank on expensive equipment and fish.

Blackwater aquariums are also beneficial to many fish species. They emulate their natural environment, which can reduce your fish’s stress levels and boost morale for them.

Why Is The Water So Dark?

When you mix water with twigs, leaves, and logs, things start to decay. A combination of bacteria and fungi begin breaking down this organic matter. When this happens, humic substances are released into the water.

Humic substances are not just one chemical compound. Instead, they’re a “soup” of all kinds of organic compounds. Humic substances are also dark brown to black in color, causing your water to look dark.

The chemistry is complex, but all you need to know is that humic substances make your water dark. 

How To Set Up A Blackwater Aquarium

Now that you understand what a blackwater aquarium is, it’s time to create one! To do this, let’s take a look at the very specific elements you’ll need.


The first thing you’ll need is an aquarium. The size does not matter. You can opt in to use a nano tank, or build a 500 gallon river aquarium!


For substrate, use a fine gravel as this works best to anchor your plants and provide a root zone. Fish also like this type of substrate, as they sift through it to look for live foods.

Be sure to use gravels designed for planted aquariums. Preferably, a light colored natural gravel substrate does best.


Blackwater habitats are naturally dimly lit and shadowy. You’ll need to recreate this. To do this, you’ll need to use colored or white LEDs with specialized settings to create light ripples through your aquarium to mimic the natural movements of light through trees.


This is an important component of a blackwater aquarium. Make sure the water is low in hardness and alkalinity. The ideal range is 2-5 degrees.

For those with harder tap water, you’ll need to blend the tap water with reverse-osmosis water(RO-Water) to get the desired hardness and alkalinity levels. You don’t need to have an exact hardness range, you just want it to be less than 8 degrees.


Your blackwater aquarium is home to tropical fish who need warmer water temperatures. I recommend you use a simple submersible heater to stabilize temperatures. You should aim for 75-80 degrees inside your tank.

Water Movement

Water movement is crucial for blackwater aquariums. Smaller blackwater fish tanks will do fine with HOB power filters for water movements. For those with larger tanks(Above 40 Gallons), you should have power heads or canister filters to provide more powerful, natural water movement.

If you have live plants, don’t go extreme on the amount of water movement inside your tank. The reason for this is because the surface of your tank contains carbon dioxide which plants need. Water movement will disrupt the surface, thus disrupting the carbon dioxide supply.

If you don’t have plants, you can have as much water movement as you desire.


Proper filtration is crucial in a blackwater aquarium.

Use mechanical filter media to capture debris. Sponges, filter cartridges, and any other type of mechanical media should be cleaned or replaced monthly.

I suggest also using activated carbon. Activated carbon will remove some of the humic substances inside your tank, which will keep the tank from becoming “too black”. Blackwater tanks need humic substances, so only use activated carbon for a week or so each month.

Creating Blackwater(Making the water dark)

Now that we know what elements we need for a blackwater aquarium, it’s time to make the water black.

To create blackwater, you’ll need to lower your water’s pH. You want your water to have a pH of about 4.5 to 7. Generally, anything under 7 is acceptable.

So how do we lower the pH?

The first step is to blend your tap water with RO(Reverse-osmosis) water. Using RO Water will help balance your water chemistry and bring your pH down.

The next step is to release tannins into your tank. There are three main ways to do this.

Method 1: Releasing Tannins With Driftwood

Driftwood is one of the best ways to introduce tannis into your blackwater aquarium. The nice thing about blackwater tanks is that you can use any kind of driftwood that’s safe for aquariums, and you don’t have to treat it first!

In fact, you don’t want to boil driftwood, because you want to release as much tannins into the water as you can.

A great type of driftwood for blackwater tanks is Manzanita wood. 

Method 2: Releasing Tannins With Rocks

Another good way to introduce tannins is with rocks. Any type of rock will work as long as it’s treated. The reason you want your rocks treated is to prevent the release of calcium, alkalinity, or microbes into the water. 

Also, be sure to avoid any jagged edges to keep your fish safe, but smooth and rough rocks work. 

Method 3: Releasing Tannins With Leaf Litter

The absolute best way to create blackwater is through leaf litter. 

A general rule of thumb is that you want to use 2-3 leaves per 20 gallons of water.

Here are the best leafs to use for blackwater tanks:

  • Red Oak
  • Turkey Oak
  • Sessile Oak
  • European Beech 
  • Hawthorn 
  • Japanese Maple
  • Pedunculate
  • Alder Cones
  • Indian Almond

Best Blackwater Plants

One of the main things you’ll need to consider is the use of plants. You don’t want to include many, if any, in your blackwater setup, or you’ll run into issues later, such as lighting and water setup. 

If you want to use plants however, you want to choose low light plants.

Here are the best low light plants for blackwater aquariums:

  • Java Fern
  • Java Moss
  • Amazon Sword
  • Amazon Frogbit
  • Anubias
  • Red Tiger Lotus
  • Water Sprite

Best Blackwater Fish

Finally, the last piece to any blackwater aquarium is finding and stocking the best freshwater fish for blackwater tanks.

The first question that pops up is “can I use betta fish?” The answer: YES! In fact, bettas are native to blackwater habitats, so they’ll thrive in a blackwater tank.

For those that are interested in fish other than bettas, here are the best blackwater fish:

  • Tetras
  • Angelfish
  • Discus
  • Neon Tetras
  • Pimelodus Catfish
  • Barbs
  • Danios
  • Red Tail Sharks
  • Gourami
  • Glass Catfish
  • Cichlids

Also keep in mind how much fish your tank can hold. Every fish tank is different, so knowing how many fish per gallon your aquarium can hold is a must!

Maintaining A Blackwater Aquarium

Just like any other type of aquarium, a blackwater tank will benefit from water changes. I usually opt in to change about 20% of the water every 2 weeks.

If the tank is getting “too dark”, I’ll increase the amount of water changed, or perform them more frequently. 

In general, keeping a consistent cleaning schedule and knowing how to clean a fish tank should keep your tank safe and clean for your fish. Just be sure not to overclean your fish tank, as this will remove most of the tannins from the water.


A blackwater aquarium is a fun challenge for both new and experienced fish keepers. 

The key to a successful blackwater tank is to take your time. Allow the natural processes to break down tannins and any other beneficial substances into the water.

If done correctly, a blackwater aquarium can be a beautiful ecosystem with colorful, vibrant fish.

Photo of author
Hey there, my name is Gunnar Kennedy. I'm a fishkeeping enthusiast who's been in the hobby for over a decade now! I love sharing new ideas and helping others care for their aquatic friends!

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