The blackwater aquarium aims to replicate the conditions found in the blackwater biotope.
Blackwater aquariums are created from a mixture of leaf litter and plants, creating a tinted water effect. The process is similar to the brewing of tea, where the properties of dried tea leaves are infused with water.
Tannins [are] a yellowish or brownish bitter-tasting organic substance present in some galls, barks, and other plant tissues, consisting of derivatives of gallic acid, used in leather production and ink manufacture.Oxford
Examples of fish native to blackwater habitats include Betta and Tetra fish.
Most tropical aquarium fish originate from blackwater habitats. Oftentimes, fish that come from both the Amazon basin and Southeast Asia, from two separate continents, will have similar care requirements because they have adapted to similar habitats.
The blackwater aquarium is brewed with dried and rotting plant matter that enters the water. This yellow color is created by tannins released into the water when the dried leaves or driftwood disintegrate.
Tannins are responsible for not just the change in color within the aquarium but also will lower the pH and soften the water. The pH level of blackwater aquariums typically ranges between 5.5-6.5 however, in some cases, they can be as low as 4.5.
In the wild, blackwater habitats provide shelter and nutrition for many fish species. Leaf litter (a component of the blackwater habitat) starts to rot over time, creating opportunities for rotifer colonies (microscopic invertebrates) to grow, from which fish fry can feed.
The leaf litter also provides many hiding areas for fry and smaller fish species, providing shelter against predators. Thus creating a symbiotic relationship between the fish and its environment.
Pretty cool, eh?
Now, you’re wondering how you can create blackwater.
There are a few ways to create a blackwater environment in the aquarium.
– Indian almond leaf
This method of creating blackwater is the preferred method as it is a more natural way of introducing blackwater.
Also known as ‘ketapang’ or ‘cattapa’ leaves, the Indian almond leaf is no stranger to the aquarium trade. This leaf comes from the Indian almond tree and is native to Asia, Australia, and Africa.
For years, hobbyists have been using this leaf to create blackwater systems for a few reasons. It is said that the tannins released by the Indian almond leaf have healing properties and can prevent fungal growth. Many experienced hobbyists swear by them.
Some fish also require blackwater to breed. As such, adding Indian almond leaves will mimic their natural habitat, encouraging spawning.
The presence of the Indian almond leaf also provides space for the fry to hide. This is important as some fishes have the habit of killing or eating their fry upon hatching. Adding the Indian almond leaf also acts as an additional layer of protection.
The Indian almond leaf is also a popular choice because it not only comes with all the above benefits but also decomposes slower than most other varieties of leaves, which means the leaves do not need to be replaced as often as another leaf might.
– Blackwater extracts
There is a variety of blackwater concentrates on the market. The Betta SPA, for example, is specially formulated to mimic the parameters found in the natural habitat of betta fish.
Just a few drops into your tank, and you can expect to see that tinted yellow glow.
However, as convenient as it may be, this method should be used carefully since it can drastically and suddenly change the biochemistry of an aquarium.
Generally, it is recommended that fishkeepers gradually insert the extracts into their aquarium.
I do not use commercial blackwater extracts. I much prefer a homemade solution. To see how I create homemade blackwater extracts, see this article.
Driftwood is also a common way of introducing tannins into your aquarium. This is the “slow-cook” method.
New hobbyists often don’t realize that driftwood can releases large amounts of tannins. It is also a common misconception among new hobbyists that once the water turns a tinge of yellow, the tank is dirty.
Below are some species of common blackwater fish:
- Neon tetras (Paracheirodon innesi)
- Cardinal tetras (Paracheirodon axelrodi)
- Guppy (Poecilia reticulata)
- Angelfish (Pterophyllum scalare)
- Corydoras Catfish (Corydoras)
- Discus (Symphysodon)
- Dwarf Gourami (Trichogaster lalius)
- Sparkling Gourami (Trichopsis pumilia)
- Cherry Barb (Puntius titteya)
When adding the leaves to the tank, you will probably notice them floating. Leave them be, and they will sink in about 24hrs. When setting up your aquarium, consider which method you will use to add tannins to the water. The easiest method is to use Indian Almond leaves. If you want to avoid leaf litter at the bottom of the tank, then using blackwater extracts is recommended. Driftwood can be helpful but can be unpredictable and inconsistent.
The leaves should be left there until they disintegrate completely because they function as part of the entire ecosystem within your tank. The leaf’s purpose is not just to color the water but also to provide macronutrients to the tank’s inhabitants. Fish and critters, like shrimps and snails, will feed on the disintegrating leaves. As an added benefit, leaving the leaves in your tank creates a great aquascape for a more natural aquarium feels.
Local fish stores will also typically have them. Alternatively, they’re available for purchase on online retail stores like Amazon and eBay.
Generally, adding these leaves into the tank does not constitute much risk, although it does cause the pH to drop slightly. A general rule of thumb would be 10 ketapang leaves for every 5 gallons of water.
But this heavily depends on how pronounced you want the blackwater effect to be in the tank. 10 leaves in a 5-gallon tank will produce a moderate tea color, and 10 leaves in a 5-gallon tank will make for a dark tea color. Remember, the more leaves you put into the tank, the faster your pH will drop and the softer your water will be. Consider the safety of your fish.