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Blackwater Fish Aquariums

Blackwater Fish Aquariums 

Reviewed by Don Spaeth

What is black water? | What is a blackwater aquarium?   | Benefits | Blackwater aquarium setup | Managing a blackwater aquarium | Embrace the challenge

blackwater fish aquarium

Beautiful, unique and even a little mysterious, a blackwater aquarium can add a special mystique to your home. Perhaps more importantly, a growing consensus maintains that a blackwater setup can be healthier for certain types of pet fish compared to a typical aquarium setup. While it can be more of a challenge to assemble, many aquarists believe a blackwater tank is well worth the effort.

What is blackwater, and where does it come from in nature?

Bodies of blackwater are found all over the world, typically in the form of ponds, temporary pools and freshwater rivers that run through tropical rainforests and peat bogs. The dark color of the water, which can range from a light tea hue to a rich coffee brown, comes from the accumulation of dissolved humic substances and plant tannins. Humic substances comprise a mixture of many different organic compounds, including peat and soil.

When a river moves into a floodplain, it picks up leaf litter, twigs, branches, fruits and seeds that all begin to decay. This decay releases the humic substances and tannins that stain the water—the more of these decaying materials, the darker the water. The release of humic substances also lowers the pH of the water, making it more acidic.

What is a blackwater aquarium?

Building a successful blackwater fish tank means mimicking the chemistry and physical structure of blackwater found in nature. Aquarists need to pay close attention to maintaining a low pH, limiting minerals in the water and adding the right balance of organic matter into the tank.

A new blackwater setup will need time to age as the organic matter undergoes the decomposition process. You should notice the color of your aquarium water darkening over time. This is a good sign the aquarium is aging well. Keeping the water chemistry at the right level takes patience, practice and some experimentation.

What are the benefits of a blackwater tank?

You may be puzzled why anyone would want to create a blackwater aquarium. The idea of putting aquatic life in dark-colored water may seem a little odd. However, there are several benefits to creating this type of aquarium for many species of aquatic life.

  • Improved health for your fish Emerging evidence is showing that blackwater tanks may enhance the health of your fish, allowing them to heal faster and resist disease better. This may be because blackwater more closely mirrors the natural environment of certain types of fish. Some aquarists have found that fish in blackwater setups are more likely to breed and showcase natural behaviors.
  • Lower maintenance needs The dark hue of the water means that algae does not grow as quickly in blackwater aquarium setups as compared to more standard aquariums. Aquarists may also find they need to perform fewer water changes and/or replace less water during each change.
  • A unique and beautiful visual With the right lighting, blackwater fish tanks can highlight the iridescent colors of your fish. Your fish will display dazzling streaks of color as they swim through the water. Additionally, adding stones, driftwood and leaves into your tank will create a soothing, natural-looking environment.
fish in a blackwater aquarium

How to set up a blackwater aquarium

Ready to give a blackwater tank a try? Here’s what you need to know about each important aspect of this type of fish tank setup:

Aquarium size

One of the best things about blackwater fish tanks is that you can choose an aquarium of any size. From a nano tank to a 100-gallon tank or larger, any size aquarium can work.

Organic matter

There are two ways to add tannins to your tank’s water—instant additives and slow-release organic sources. Some of the best organic substances to add to your blackwater tank include:

  • Peat Mix peat into your tank’s substrate or add a mesh bag to the aquarium filter.
  • Driftwood The right type of driftwood will slowly release tannins for months or even years. The best types of driftwood for blackwater aquariums are Malaysian driftwood and Mopani wood.
  • Indian almond/Catappa leaves These leaves are relatively easy to obtain. Just scatter a few at the bottom of the aquarium and replace them each month. Don’t worry if they float on top of the water at first—they’ll eventually sink to the bottom. Indian almond leaves are also an excellent addition to any betta tank setups, whether they’re blackwater or not.
  • Alder cones These cones are the catkins of black alder trees. They are another good source of humic substances.

Aquatic life

Over 200 species of freshwater fish—and some invertebrates—live in natural blackwater environments, which means you have a lot of choices when it comes to populating your aquarium. As always, do your research before adding aquatic life to your habitat. Some blackwater fish grow quite large—a pacu typically grows to be over 2 feet long—while others don’t play nicely together. If you add firemouth cichlids and tetras into the same tank, your tetras may begin disappearing fast.

Some of the most popular fish for blackwater tanks include:

Water

The key to a successful blackwater setup is good aquarium water care. You need to maintain soft, acidic water in your tank. Ideally, this means a range of 2 to 5 degrees of carbonate and general hardness and a pH less than 7. In nature, blackwater can reach levels as low as 4.5 pH, but this isn’t realistic for most aquariums. If your tap or well water is too hard—a common challenge—utilizing reverse osmosis or distilled water will help lower the hardness.

Adding the right types of organic plant matter to your tank will slowly lower the water’s pH, but if you need to lower the pH more quickly, use a commercially available instant blackwater additive.

Substrate

Choose a substrate that is either pH neutral or rich in organics that can add to the humic substances and tannins in your aquarium. Look for acidic clays or soil substrates. Fine gravel is another option, as it can also provide a place for live plant root growth.

Stay away from marine sand or gravel—usually made from crushed aragonite or limestone—as these substances can increase your water’s pH and hardness. Freshwater sand and gravel are pH neutral and are a better option.

Lighting

Most types of lighting will work in your blackwater fish tank if you don’t plan to include live plants. If you do want to incorporate live plants into your aquarium, a full-spectrum daylight-style LED fixture may be the way to go. Brighter light will also give you better visibility and can create some beautiful effects, such as light ripples that replicate sunlight dappling the water.

Heater

A submersible heater will work for your blackwater tank. Keep water temps in the range of 72 to 82 degrees Fahrenheit, depending on the species.

Filtration

Filtration can be tricky in a blackwater aquarium. Typical aquarium filters are designed to remove organic matter, but you need this matter to create the proper blackwater chemistry. Also, a high level of decaying plant matter in your tank can quickly wear out your filter.

If you decide to use a power or canister filter, take out the activated carbon, which would otherwise remove the organic matter in your tank. You can replace the activated carbon with peat or sponges.

Plants and rocks

Plants and rocks, along with other tank décor, can add extra decoration and creativity to your aquarium. Research any rocks before adding them to your habitat to ensure they won’t add calcium or carbonates to the water—these will increase hardness and lower acidity, respectively.

Live plants aren’t required in a blackwater tank, but they can look vibrant and lovely sitting on top or in dark water. If you want to add live plants to your tank, look for plants that can handle medium or low light. Some popular plant options are:

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Managing a blackwater aquarium

With patience and perseverance, you can recreate natural blackwater conditions in your fish tank. The work doesn’t stop there, however. As with any aquarium, you’ll need to continually monitor and manage your water conditions.

With a blackwater tank, you’ll need to regularly monitor the water for:

Water testing kits are a must to ensure you maintain proper water chemistry for your blackwater fish. Your local Petco Pet Care Center also offers free water testing.

Perform water changes every two to four weeks, replacing around 10-25% of the water at each change. Be aware of the hardness of your home water and mix your new water with reverse-osmosis or distilled water if needed.

Monitor the pH of your water after each water change. If the pH rises too high, a few drops of an instant blackwater additive can help bring the pH back down to a healthy level. Petco offers a range of aquarium water conditioners and additives that can help you better manage your tank’s water.

If you notice the water in your tank getting too dark, you can increase the frequency of your water changes, change out a larger amount of water during each change or add activated carbon to your aquarium filter.

Embrace the challenge of a blackwater fish tank

If you are ready for a challenge and want to create a truly unique aquarium, a blackwater tank is a great option. Petco offers all the solutions you need to set up and populate your blackwater aquarium. Our Pet Care Center aquatic specialists are happy to answer any questions you have—whether you want to create a blackwater tank or want to know more about saltwater aquariums, tanks and kits.

Reviewed by Don Spaeth

Don is Petco’s National Aquatic Care, Education and Programs Manager. He is an avid aquarist who has worked with and cared for freshwater and marine aquatic life for over 40 years. Throughout his 27+ years with Petco, Don has actively been involved with our aquatic vendor partners and worked to promote aquatic education both in store and company-wide.

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