Blackwater Aquarium: How To Set Up Your Biotype Tank

If you are looking for an exotic aquarium idea, you might want to consider setting up a blackwater aquarium. These tank set-ups offer a unique take on the traditional aquarium environment — and can be simply amazing to look at. 

But what exactly is blackwater, and how do you set up a blackwater aquarium? Well, this article will explain both of these things — and explore the plants, animals, and environmental variables that can help these aquariums thrive. 

What is Blackwater? 

Blackwater is a term that references the type of water found in blackwater rivers. Blackwater rivers are slow-moving, slightly acidic water bodies found in tropical forests, swamps, or wetland areas. 

Blackwater river water is transparent in appearance but also has a stained black (or brown) color. This color is said to resemble black tea — and is the result of decaying roots and leaves from the surrounding environment. 

Plant decomposition causes the leaching of tannins (phenolic or gallic acids) into the water. These substances are composed of carbon, oxygen, and hydrogen and decrease the river’s pH levels — making it more acidic. 

It is common for blackwater to have more aluminum and less calcium, magnesium, sodium, and potassium than faster-moving whitewater, clear water, or marine environments. The tannins also give the water an ironlike brown appearance. 

Blackwater rivers are typically found in Amazon rainforest river basins and the southern United States. As an environment that originates in tropical areas, examples can be found throughout Africa, Asia, and Australia. 

Though blackwater has a chemical composition that benefits many fish and plants, some animals do not thrive. For example, there are comparatively fewer snails and crustaceans in blackwater, owing to the low calcium content needed to sustain their shells. 

What is a Blackwater Aquarium? 

A blackwater aquarium is an aquatic tank set-up intended to resemble the environment of a blackwater river. Blackwater aquariums focus highly on blackwater water chemistry caused by plant decay, down to pH, GH (calcium and magnesium), and KH (alkalinity) levels. 

Blackwater aquariums can be of all different sizes. There are some contained in nano tanks as well as others in full room-length tanks. What keeps these aquariums similar is their live and decaying plants, fish, temperature, lighting, chemical composition, and gravel components. 

How to Set up a Blackwater Aquarium 

To set up a blackwater aquarium, you must determine what kind of environment you would like to create. Some hobbyists like to create aquariums that replicate actual black river environments, like the Amazon or the Orinoco river basin. 

Other hobbyists choose to create an environment with mixed qualities, including plants and animals from different ecosystems. This is entirely up to the hobbyist, but research is recommended for specific combinations of species. 

In general, though, a blackwater aquarium is typified by soft, dark, acidic water with a pH level a little below 7. Though a 4.5 pH level is typical in the wild, levels around 6 – 7 are common in most home blackwater aquariums. 

This pH level is achieved through the boiling of Adler cones, Indian almond or oak leaves, and driftwood — making an “extract” that can be diluted and used as aquarium water. These decayed plant materials can alternately be placed at the bottom of a tank, leaching tannins into the water over time. 

Here is a step-by-step guide to set up your blackwater aquarium.

Step 1: Driftwood 

Driftwood is a must-have for blackwater aquariums. It is exemplary of the type of organic material that is found in wild blackwater river environments. 

You can use different driftwood types in your tank, including Manzanita, Mopani, African, and Malaysian driftwoods. The better you know the environment you are trying to recreate, the easier your choice will be. 

Driftwood is normally placed first into an empty tank and is positioned to reach a practical and aesthetic arrangement.

To prepare the driftwood for use in your tank, you must boil it. Get a usable pot large enough to fit your driftwood inside and fill it so that the water covers the wood. Then let it boil for 1 to 2 hours and let cool. 

Alternately (because driftwood will often float in boiling water), boil one side of the driftwood for 15 minutes. Remove from water and rinse. Then change the pot’s water, put the unboiled part of the driftwood inside, and boil again for another 15 minutes. 

Always let the driftwood cool completely before adding it to an aquarium. It would help if you had a rough idea of how you want your driftwood to be arranged in your tank before placing it inside. 

Once the driftwood is inside the tank, you can add water. It may take a while before the driftwood completely soaks up water (so it does not float). This will take about one or two weeks — so you may want to place the wood under a rock in the meantime. 

Step 2: Substrate 

Next, a layer of silt is placed on the bottom — which can be used to keep the driftwood in place. 

Blackwater environments are composed of silt, a combination of feldspar, quartz, and decomposed organic materials. Silt is typically rougher than clay — but finer than sand — with its particles being 0.002 – 0.05 millimeters in diameter. 

For a blackwater aquarium, fine gravels of light or dark colors are recommended. Sand is considered too fine a substrate layer for a blackwater tank — besides this, the fish species that dig for food at the bottom of these tanks usually sift through gravel. 

Step 3: Leaf Litter and Cones 

The most essential part of a blackwater aquarium might be the organic parts that leach tannins, humic acid, and fluvic acid into the water. For these, particular tree leaves and cones must be placed on top of the substrate. 

In terms of leaves, they should be dried leaves of particular species. 

Indian almond leaves, Japanese maple, Hawthorn, Sessile oak, Turkey oak, European (English) oak, Red oak, and European beech can all be used. Indian almond leaves are trendy among hobbyists, and like these other dried leaves, they are available in stores.

It is recommended to have two leaves for every ten to fifteen gallons of water in your tank. 

Like wood, these leaves will take a while to become completely soaked with water to the point of sinking. This will take about a day or two. Make sure to change your leaves every 1 to 2 months, and monitor your water’s chemical levels. 

Step 4: Water

Blackwater aquariums need to have soft water (low on calcium, magnesium, and carbonate/bicarbonate ions). Ideally, they should have a pH level of around 6.5 to 6.8 (though some sources say as low as 5.5 to 6.5 pH). 

Lower pH levels (higher acidity) can result in acidosis in fish, damaging their gills and internal organs. Higher pH levels (very alkaline water) will not adequately recreate blackwater environmental conditions. 

Similarly, hard water will contain too many minerals. This is also something blackwater does not naturally have. 

Ideally, soft water for blackwater aquariums would be below 4 to 8 dKH (degrees of carbonate hardness) and 4 to 8 dGH (degrees of general hardness). You can use reverse osmosis filters to lessen water hardness, often in conjunction with some proportion of dechlorinated treated tap water. 

So, in summary, you will want soft, mildly acidic water with anywhere from 5.5 to 6.8 pH. You will also want dKH and dGH levels to be under 8, ideally between 4 to 8 dKH/dGH. 

Once the treated tap water has been added (to about 7/8ths of the tank), the extract from Alder cones and leaves can then be filtered into the tank, giving it a characteristic brown color. An aquarium filter is then run for several days to clear the water, which initially may be murky. 

After a few days of filtering, the water will appear to be clearer. At this time, live plants, fish, and invertebrates can be added, completing the blackwater aquarium. 

Step 5: Lighting 

When lighting a blackwater aquarium, a low-level LED aquarium light or single fluorescent tube light is recommended. In wild blackwater environments, light filters through the forest canopy — reaching the water in limited amounts. 

Blackwater aquarium hobbyists like to replicate the Igapo “swamp forest” environment of the Amazon. In this environment, trees are completely inundated with water for most of the year, with light being scarce at their roots. 

This, however, is not a necessary lighting condition for many blackwater-friendly plants (like anubias, Java ferns, bucephalandra, and dwarf aquarium lillies). In this case, a medium-low LED light (60 PAR or less) would suffice. 

Step 6: Heater 

For blackwater aquariums, most tanks require an internal temperature from 75 to 80 degrees Fahrenheit. Some tanks will require higher temperatures than others, with steady temperatures around 78.8 degrees reported. 

A submersible aquarium heater would work as well as a built-in or inline heater. If you are fortunate to have a separate fish room, you can heat this room to a temperature of 76 to 78 degrees. 

Step 7: Filter 

As blackwater aquariums often house a lot of driftwood, decaying leaves, and other organic materials, the water will tend to become tinted over time. For this, it is recommended to use an activated carbon filter for one week out of every month. 

If you are using filter cartridges, sponges, or power filtration systems, you should replace or clean these at least once every month. Some sources recommend a sump over a hang-on-back filter. 

Some synthetic polymer products remove ammonia, nitrates, and nitrites — without removing substantial amounts of tannin. These products must be placed inside a media bag and placed inside high-flow areas of a HOB (hang-on-back) filter. 

Step 8: Rocks 

This step is optional and based on personal preference.

In blackwater aquariums, you will want to avoid rocks that release too much calcium or magnesium. This includes rocks like limestone, marble, and mafic igneous rocks (basalt, gabbro, and diabase). 

Blackwater rivers tend to have rocks made primarily of quartz, sandstone, clay, and like materials. For this reason, you can use shale, slate, quartzite, and lava rock in a blackwater aquarium. 

Best Fish for a Blackwater Aquarium 

The fish for your blackwater aquarium will ideally be fish native to the blackwater river environments you are trying to recreate. These fish are often categorized by region. 

If you are trying to recreate a South American environment, you will want to use fish like corydoras catfish, common hatchetfish, angelfish (Pterophyllum), neon tetras, cardinal tetras, discus (Symphysodon), Farlowella, Dwarf cichlids, and armored catfish (Loricariidae). 

If you are trying to recreate an Asian environment, you will want to use fish like Paradise fish, wild bettas, glass (ghost) catfish, gouramis, red-tailed black sharks, slender danios, and the Ghost knifefish. 

If you are going to combine different regional fish species, it is best to know each species’ temperament. Some species can become aggressive (like blue gouramis to angelfish), so look into species that can get along. 

Best Plants for Blackwater Aquarium 

Like fish, plants in a blackwater aquarium can be region-specific. However, the line blurs for many hobbyists as they attempt to make more composite ecosystems. 

Strictly speaking, the Igapo “swamp forest” water is normally devoid of smaller live plants — but species like Amazon sword, Amazon frogbit, and Brazilian Pennywort are found in adjacent environments. These species can be cultivated in blackwater aquariums. 

Asian blackwater plants include Cryptocoryne, Java moss, Java fern, Bucephalandra, Water sprite (Ceratopteris thalictroides), and Christmas moss. Though their distribution is over a wide range, these plants typically grow in tropical slow-moving freshwaters. 

Anubias are a species of flowering plants that have their origins in western and central Africa. Although this is the case, they make a good all-purpose semi-(or completely) aquatic species for blackwater aquariums. 

Maintaining a Blackwater Aquarium 

It is necessary to keep in mind several factors when maintaining a blackwater aquarium. You must keep an eye on your water, fish, substrate, live plants, decaying plants, rocks, and environmental variables. 

For your water, make sure that your pH and dKH/dGH levels are suitable, and your filter is running constantly and adequately (replace as necessary). Keep an eye on tannins, and remember that blackwater is meant to be somewhat clear. 

For the fish, you need very low saline soft water, an established filter (preferably there for four months between cleanings), a UV unit (to kill bacteria), and a strong sump-type filtration device (ideally). Bacteria are the primary concern for fish in blackwater environments — and these practices can mitigate their effects. 

For the substrate, use a siphon-powered gravel cleaner once every other week, if not more often. This should go in tandem with cleaning your tank and water changing. 

Live plants require lighting at least 12 hours a day, liquid fertilizer, CO2 levels lower than 40 mg, and 25% water changes every other week. 

Decaying plants (driftwood and leaves) especially leaves — will need to be replaced every month or two. Monitor your water levels for humic and fluvic acids, tannins, and changes in pH levels. 

To clean rocks, you may first want to consider keeping as few rocks in your aquarium as possible. This will help reduce the amount of upkeep and possible fish food lost under such fixtures. 

However, you can always remove rocks and clean them with warm water and an algae scraper. In this case, round, smooth sand-based stones may be a good idea for your blackwater tank. 

Finally, you will want to be observant of your blackwater aquarium’s overall health. Besides looking at variables like a steady temperature and pH levels, look to see if your fish are clean and healthy-looking. 

Look out for fish that may be swimming slowly or erratically — this may be the first sign of disease. Check to see if your live plants are healthy, growing, and not overexposed. 

Contrary to what you may think, you might have to clean a blackwater aquarium more often than a normal freshwater or saltwater aquarium. The warm, slow-moving water makes a ready place for bacteria and algae to grow. 

Do not be afraid to make slight adjustments to experiment to get your water to ideal levels. Also, ask around. Chances are, the trial-and-error experiences of your fellow hobbyists will prove invaluable. 

Final Thoughts 

Blackwater aquariums are a challenging endeavor to even experienced aquarium enthusiasts. The right balance of wildlife and environmental variables can be difficult to obtain without adequate information. 

However, with the right research, careful planning, and a lot of hard work, you can create a successful, worthwhile blackwater aquarium. The extra effort adds to the appreciation of this unique aquarium environment.

Looking for tips about aquarium maintenance? Head over to our Aquarium Maintenance & Repair section to see more.

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