Blackwater Aquariums

Blackwater Aquariums: Are they Worth Trying?

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When it comes to aquariums, most minds instantly think of crystal translucent water tanks. Although, this is not actually the type of environment that most fish we keep naturally live in. 

A lot of water bodies out in nature have a dark color by decaying organic material. And there are various fish species that prefer something similar in the tank. That’s how blackwater aquariums become popular. 

A blackwater aquarium is an ideal environment for your aquatic life to flourish. In this article, we are pleased to help you understand more about blackwater aquariums and show you how to set up your own one as well. 

What is Blackwater? 

The Amazon River and its tributaries are categorized as whitewater and black water. 

Whitewater habitats get a neutral pH of about 7.0. The water contains suspended particles and a lot of nutrients. The whitewater habitat is comparatively transparent. 

Meanwhile, blackwater habitats have dark-colored, clear water produced by wide amounts of dissolved humic substances dissolving into the water. This is because the rivers surge and extend into floodplains. If the floodplains occur to be a forest with much leaf litter, the water will be acidic and stained by decomposing wood, leaves, fruit, and seeds. 

This niche habitat is known as “root forest” in Brazil. The twisted tree roots and humic acids form a distinct freshwater habitat that is home to more than 200 fish species. 

As you combine water with leaves, logs, and twigs, things begin to decay. A mixture of chemical and biological (bacteria and fungi) processes start affecting the organic matter. Humic substances in the plant material are leaked into the water. 

Humic substances are not just a single chemical compound in nature. The water carries a literal mixture of all types of organic compounds. Humic acids have a dark down to the black color, while fulvic acids are more yellowish. 

The chemistry is complicated, but all you need to know is that these natural compounds stain the water and help decrease the pH. 

What is a Blackwater Aquarium?

How a Blackwater Aquarium Looks Like

The original idea behind blackwater aquariums is to emulate the water chemistry of Amazonian blackwater and have physical features of the Amazon. In other words, the tank water needs to be low in minerals and aquascaped with live aquatic plants, organic matter (leaves), and aquarium wood that will decompose. 

The aquarium will age gradually, which means the decomposing plant material will produce natural acids and other compounds, making the water turn tea-colored. 

A blackwater aquarium is like a planted one. The primary task is preserving the habitat for the plants with a controlled decomposition of leaf litter. 

As usual, acid-loving freshwater fish are put to bring color, movement, and interest to the aquarium. Besides, the fish also provide nutrients and contribute carbon dioxide for the plants, building a balanced ecosystem.

How to Set Up a Blackwater Aquarium? 

Set Up a Blackwater Aquarium

Aquarium size 

It does not matter what size of your tank is. You can buy a nano tank or establish a 500-gallon river aquarium. 


Fine gravel (not sand) will work properly to anchor plants and bring a root zone. A lot of Amazonian fish species love to sift sand while searching for live foods. You can choose light-colored natural gravel or a darker specialty substrate for planted tanks. 

Water chemistry 

It is essential to consider the chemistry of the water as a real blackwater aquarium has soft acidic water. 

Whereas the tannins may help slightly reduce the pH, you might need to look into using reverse osmosis water if your tap water is too hard. 

It sounds unrealistic to match the real pH of blackwater rivers and streams, but 7 or lower is a great condition if you want to make your fish and plants feel like they’re home. 

You can get the blackwater look in your aquarium by adding leaves (Indian almond or oak), alder cones, or driftwood. 

Leaves and alder cones can be boiled, soaked, and filtered to generate a strong blackwater “extract”, but you can also scatter them along the bottom of the aquarium, and they will eventually darken the water as they would in a natural stream or rival. 

Water movement 

With a small-sized tank, a hang on the back-power filter may offer all the water movement you need. For bigger aquariums, you can use a canister filter or powerheads to generate a flow of water throughout the tank. 

If you are keeping live plants, remember not to agitate the water surface too much. It will remove the carbon dioxide plants need. If there are no plants, you can freely aerate the water as much as you like. 


Your blackwater aquarium will be home to tropical fish who need to live in a warmer water temperature. Therefore, it is highly recommended that you use a simple submersible heater to stabilize the temperature in the 75 to 80 degrees Fahrenheit range. 


Being under a forest canopy, the blackwater aquarium is naturally dimly lit. If you are not going to use live plants, almost all types of aquarium light will work. Ideally, you will want to use colored or white LEDs to see into the tea-stained tank. 

Moreover, white LEDs produce light ripples throughout the aquarium, just similar to sunlight passing through the forest trees. If the fixture has specialized settings adjusting the color spectrum, you can experiment to identify which color blends brings out the colors of your inhabitants. Various aquatic plants will flourish under medium-brightness LED lighting as well. 

pH level 

In nature, the pH of natural waters can vacillate ferociously during the course of 24 hours. In the morning, the pH can be at 5, increase to 9 at noon and decrease to 5 in the evening. This normal increase and decrease are not stressful or detrimental to fish.

In a tank with low alkalinity, it will be natural for the pH to fall because of natural acids released via the biological filter. The humic acids will help to reduce pH, but they are not “strong” acids. They will not affect the pH if your alkalinity is high. It is possible to maintain the aquarium below pH 6. 

If you don’t have much experience with aquarium water chemistry or don’t want to keep an eye on pH and KH levels, hold the pH between 6.5 and 7.0 by balancing the carbonate hardness in tap water with pH in your aquarium. 

In the meantime, if you want to test the water and implement small changes in water chemistry, you can run the aquarium with 1 degree of alkalinity and maintain a pH around 5. Tropical fish species will color up in an acidic environment as long as they are provided with a balanced diet. 

You can consider using these test kits for monitoring your water chemistry:

  • Water hardness (GH & KH) test kit 
  • Low-range pH test kit 
  • Ammonia & Nitrite (for periodic tracking of biological filtration)


Using mechanical filter media is a good idea to catch debris. In addition, you necessarily clean or replace sponges, filter cartridges, and other sorts of mechanical media on a monthly basis. Activated carbon will get rid of some of the humic substances. 

You can use activated carbon every week or every month only. If your aquarium appears too dark to your favorite, use more activated carbon and change it every week to decrease the staining of the water. This will eliminate some of the humic substances and other undesirable organics that appear in the water. 


Aquarists can use smooth stones and rough rock to build a river bed or jagged outcropping. You must select rock that won’t give off alkalinity (carbonates) and calcium (water hardness).

Some rocks will boost the pH by slowly producing carbonate hardness (KH) into the water, so do deep research before you buy rocks. 


Remarkably, you can use any type of aquarium driftwood that is safe for the aquarium and is not known to increase pH. It brings into a natural look and provides fish a place to explore. Some aquarium driftwood might emit tannins to the water. 

Manzanita driftwood will be an excellent option for your blackwater aquarium that is pH-neutral and stunning-looking. 

Leaf litter 

You must be cautious when putting leaves in your aquarium. You will not want to add any leaf you pick on the ground. 

Indian almond leaves are available online and are safe for your tank. Alder cones can be used to raise tannins. Many reports these drive native trees are safe and efficient in the blackwater biotype: 

  • Sessile oak
  • Red oak
  • Turkey oak
  • Pedunculate
  • Hawthorn
  • European beech
  • Japanese maple 

You can also find prepared liquid “blackwater” additives. However, it is not proved whether these formulations have the same advantages if the natural humic substances created in the tank. 

Just as a product makes your aquarium dark does not mean its has all the characteristics of humic and fulvic acids. 

Which Fish Species Love Blackwater Aquariums? 

Fish Species Love Blackwater Aquariums

While the major part of the setup is concentrated on the water chemistry and plants, there is plenty of fish thriving in a blackwater environment. 

There are more than 200 species of freshwater fish that live in natural blackwater environments. You will have a wide range of choices for your tank. Several of these species can grow quite big; make sure to do research before picking the fish. 

Here are some of the most prevalent that will grow well in a blackwater aquarium:

  • Tetras (neons, cardinals, and others)
  • Firemouth cichlids
  • Brycon species
  • Loricariid catfish
  • Geophagus
  • Discus
  • Uaru
  • Gouramis
  • Geophagus
  • Pimelodus catfish 
  • Corydoras
  • Loricariids
  • Farlowell

Most aquarium hobbyists decide to go with smaller schooling fish such as tetras and some brilliant catfish. Discus and angelfish develop well in a planted blackwater aquarium. Plus, dwarf cichlids also thrive in this sort of aquarium. 


A blackwater aquarium is interesting and challenging to both novice and experienced aquarists. The key to having a speechless blackwater tank is to take your time. Let natural processes break down the leaves and emit the beneficial substances into the water. 

It does take more time and effort to balance the proper water conditions of blackwater aquariums. However, it will be more exciting and tempting to pursue something difficult, won’t it? Let give it a try and build a breath-taking blackwater aquarium for your home. 


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