Blackwater aquarium, tank, guide and aquascaping

Black water aquarium, tank – definition, origin, biotope.

Keeping aquariums, a  recreating natural habitat  is something amazing. Having a piece of nature at your home or office is something extraordinary.

Blackwater aquariums are getting very popular among aquarists. Not only because they look cool, but because they bring many beneficial features, like: softening the water, antibacterial, lowering hardness of water and ph. Helping with breeding fish. Even betta fish keepers use catappa leaves (almond leaves) to help their betta grow to their full potential.

 The black water aquarium is a term used for a setup with the water so dark from tannings, that fish might become very little visible. In the wild for example Black Earth creek or Eagle Creek in Wisconsin, the fish thrive in softer acidic waters, especially when the river runs thru the forest.

The river there has a reddish color due to the amount of clay in the substrate and iron level. Leaves, branches, seeds, cones, are falling into the water and produce tannings and humic acid softening the water. In the Amazon basin in Igapo region it happens on a huge scale. However, the soil over there is sandy and not rich in nutrients. Plants had to develope the skills to get use to this kind of conditions and utilize the nutrients from what they have.

In order to recreate Amazonian black-water condition in your blackwater aquarium it is good to get familiar with the most known Amazon blackwater region – ‘Igapo/gapo’.

 Igapó ‘root forest’  in Brazil known for blackwater flooded forest. This part of the tropical world is being flooded for most of the year with the dry and wet season. In the wet season it looks more like a swamp with submersed plants and tree roots.

These freshwater rivers climate ranges from subtropical to tropical. It was classified into 3 different regions depending on what type of water floods it. I would like to focus on the blackwater conditions which occur in Igapo forest. In this region trees could be under water even for 6 months, because of the amount of rain falling during the wet season. It is not the easiest environment for plants and fish, however they acclimated there amazingly. Below you can watch South American amazing black water aquarium setup.

Characterization of black water conditions in the aquarium, tank

In the nature the ph is very low about 4.5 and it would be extremely hard to keep the fish in your aquarium in such conditions. Also with highly acidic water the denitrifying bacteria will have a hard time to spread toxic ammonia to less toxic compounds, therefore you will be dependent on other materials like zolites and other chemical absorption media to remove toxic ammonia from your aquarium water. In my opinion the lowest you should be be keeping your ph between 6-7. Temperature is relatively steady 26 Celcius 78.8 Fahrenheit.

General hardness is affected by minerals, mainly calcium in your water, substrate and rocks, which can add to the buffering capacity of the water and potentially neutralize or at least impact the influence of the acid-producing materials in the aquatic environment.

Just when the water is a tea color it does not mean that is soft or acidic right away. It’s the amount of humic acids dissolved in the water and fluvic acids which has the biggest impact on it.

 The black water conditions  I would like to focus at the most are in the Curua River, Caxiuana National Forest, Para. The study says that the pH of the water is about 4.5 with relatively high Iron level. The electrical conductivity is less than 20 us (siemens) per cm. To your knowledge high quality deionized water has a conductivity of 5.5us/m at 25C and typical drinking water ranges from 5-50. conductivity is linked directly to the total dissolved solids (T.D.S.).

chemical components of soil in brazilian amazon blackwater

Source: Randall W. Myster – Igapo (black-water flooded forests) of the Amazon basin

Soil in blackwater  Curua River

 Black water soils  are sandy and acidic with low amount of nutrients. ‘The black’ color of water is due to acidic organic humic substances (tannings) that dissolve into the water from botanicals such as wood, leaves and seed pods. Bacteria and fungi helps speed up decomposition process. Low ph of water lowers ph of the soil itself. Let’s focus on mentioned before Curua River. The soil sample consist 13 g/kg of thick sand, 10.375 g/kg of fine sand, 873.4 g/kg of silt and 103.75 g/kg of clay. It would explain of the high iron amount. Let’s look at the table 5.3

brazilian amazon blackwater igapo forest study

Source: Randall W. Myster – Igapo (black-water flooded forests) of the Amazon basin

But what is silt and how is it different from the sand? Silt is something between sand and clay made of quards and feldspar. It is a fine sand, clay or other decomposited material which settles down as a


slit soil sediment in blackwater aquarium



soil particles in sand, silt and clay


Comparing the grain particle size the silt has a medium diameter between sand (with the biggest diameter) and clay (the lowest diameter) being like a playdoh while in contact with water.


Comparison of the Varzea and Igapo region

Comparing the two flooded forest regions of Amazon   – the Varzea (which is flooded by a white rivers) and Igapo forest (flooded by a blackwater rivers), the Varzea is more rich in nutrients and Igapo has less suspended inorganic elements. That is why the Igapo tends to lack in animals diversity and plants biomass compering to the other region. The tannings carry organic material called humic and fulvic acids. The Igapo forest does not receive a seasonal inflow of sediments loaded with nutrients like the whiteriver Varzea. However, it has highest phosphorus levels. All this tends to create the anoxic conditions which is a limiting factor for the plant growth.

‘Varzea is characterized by a greater richness in nutrients while igapo by acidity and nutrient poverty related to quality of its substrate or soil (movement of water brings and removes sediments often). Igapo forests in caxiuana national forest are mainly located on the banks of the carua river and caxiuana river. Those contain high concentration of humic compounds, low concentration of disolvedoxygen due to the low abundance of photosynthetic organisms in the water. Low conductivity indicating poor salt water, high amount of dissolved organic matter and acidic ph due to high content of organic acids from the decomposition of organic mater of terrestrial origin. Strongly influenced by the intense soild weathering of the drainage basin, mainly consisting of kaolinite, resulting in the prevalence of NA2+ions in these rivers.’

‘Soil is classified as silt textured  gleysol with low drainage, poor in nutrients. Gleysol is formed of recent sediments. Granulometry of this soil is predominantly formed with clay and mainly silt fractions. Igapo forests are characterized by the great abundance of ruizterania albiflora, carapa guianesis.

Changes in environmental conditions, whether intentionar or unintentional, affect all abiotic and biotic components. High spatiotemporal physical complexity provides habitat for a very high biodiversity – controlled by flood pulse. ’

Source: Randall W. Myster – Igapo (black-water flooded forests) of the Amazon basin

Have in mind that the decomposition of leaf litter seed pods and driftwood will lower your water ph, so if you will add too much of it at the time you might run into a trouble if your water is already quite soft. With the softer water the humic acids will have much bigger impact on ph than if you would use a harder water. Therefore if you are using RO water remember to remineralize it and add some hardness to it.

‘Negro river, the largest black-water tributary of the Amazon, has soils naturally rich in mercury (Hg) that is leached to the aquatic ecosystem by pedologic processes. The flooded areas of its basin are conducive to mercury methylation. Therefore, highest mercury concentrations have been observed in its black-water.’

Amazonia is the most diverse forest of the world, with also an intense energy and carbon cycle exchange among the global ecosystems. Researching it brings us to better understanding of carbon balance studies about organic and inorganic carbon, including soil, atmosphere, plant, decomposition, deforestation, fire, logging and river carbon emission/sink, the quantification of carbon balance in one ecosystem is still very difficult, especially in the Amazon region.


Plants species in Black-Waters of the Amazon

Black water conditions might be harsh for many plants. Many of them also adjusted to those conditions and thrive quite well. Most common plants and trees in the blackwater flooded region are:

  • Acai Palm
  • Buriti (moriche palm)
  • Urticaceae (stinging nettle)
  • Rubiaceae (coffee)
  • Spurges
  • Cecropia Membranacea
  • Sapium Glandulosum
  • Pauromma,
  • Guianensis
  • Byrsonima Arthropoda
  • Legume tree
I was able to find some of the botanical online. The things I was looking for to recreate the amazon blackwater aquarium were available in Ohio 614 Botanicals. Stuff like: Dregea Pods, Coco Palm Bracts, Dysoxylum Pods, Mokha Pods, Kachnar Tree Pods.

Blackwater aquarium black spider wood and botanicals - Dregea Pods, Coco Palm Bracts, Dysoxylum Pods, Mokha Pods, Kachnar Tree Pods

Remember you don’t have to add live plants while creating biotope of blackwater in your aquarium, but if you choose to do so, the plants which you could use in the aquarium to as an addition to home made blackwater aquarium, tank are all sort of low light plants such as:

  • Anubias (araceae family), barteri, afzelii, gigantea, gilletii, gracilis, hastifolia, heterophylla, pynaertii
  • Java Fern (leptochilus pteropus – microsorum pteropus)
  • Amazon Sword (Echinodorus grisebachii)
  • Floating plants – amazon frogbit ( limnobium laevigatum), water lettuce,
  • Cryptocoryne (affinis – araceae family)
  • Water sprite (ceratopteris thalictroides)
  • Cabomba (cabombaceae – fanwort)
  • Red tiger lotus (nymphaea zenkeri)
  • Bucephalandra
  • Echinodorus family
  • Emersed growing plants like hydrocotyle tripartita japan (apiaceae family) on top of the water sitting on the piece of wood with roots going down the water or Brazilian pennywort (hydrocotyle leucocephala).

Plants species growing in the flooded area shows a different type of phenological, anatomical, physiological and morphological adaptations in leaves, steams and roots in order to survive periodic floods.

Blackwater aquarium, tank leaves

The most popular are Indian almond catappa leaves. It will lover ph and soften water. There are also other leaves you could add to your blackwater aquarium. However, remember not to put any other leaves in the aquarium as they might not to be suitable for it and kill your inhabitants. Below list consist native trees leaves which you could use:

  • Pedunculate Oak – Quercus robur
  • Sessile oak – petraea
  • Turkey oak –  cerris
  • Red oak –  rubra
  • European beech – Fagus sylvatica
  • Hawthorn – Crataegus monogyna
  • Japanese maple – Acer palmatum
You can add those leaves directly to the tank after a previous preparation for example by boiling them, (killing bacteria or potencial fungus and hitchhikers) or if they are already dried out on the sun. You can make a water solution by soaking it for some time and when the water is tea colored you can add it to your aquarium as your own water additive.  Home blackwater aquarium  is a little different than what it might be in the nature, however remember if you would like to imitate the best a natural conditions, do not add too much leaf litter, as in nature the trees which are in that region does not supplement as much leaves into the water.

Another popular leaves are: Malaysian bamboo leaves, Malaysian yellow mangrove leaves, loquat leaves, jackfruit leaves, Malaysian mulberry leaves, catappa leaves, texas oak, magnolia leaves, guava leaves, 

or seed pods such us: cariniana pod, sterculia pod, alder cones, monkey pot, dregea pod, bael tree pod, dysoxylum pod, mokha pod, indian casuarina cones, lotus seed pod, kurrajong pod, lotus seed pod, calotropis pod, cocoa curls fiber, kielmeyera pod, parviflora pod, birch cones, jacaranda pod, puberula pod, pyrifolium pod, split mokha pod, sky fruit pod, magnolia seed, helix pods, isoberlinia pod, nypa palm flower, nypa palm pod, schima pod, sappanwood, kachnar tree, afzelia, swietnia, mangrove palm pod, pandanus, betel palm pericarp, poinciana tree pod,

More about using any old leaf‘  

If you are not sure how much to add stick to the general formula, for example: for a 10 gallons aquarium you could add 2 bigger almond leaves and replace it every 30-60 days. You could boil some other leaves and some pieces of driftwood and mix it in the substrate, that will decompose slower and leech longer over time.

Fish Species Living in the Blackwater

Lower light intensity in black-water conditions helps with the fish stress levels and is desirable while breeding some of the fish species. It is because some eggs are extremely susceptible to bacteria and the black water conditions tend to prevent it. I would like to mention fish species living in the blackwater conditions both suitable and not suitable for aquariums. It will help you understand what features they developed in order to survive and successfully breed in such conditions. Some of them are:

  • Peacock bass (South America)
  • Barred shovelnose catfish (South America)
  • Brycon (trout looking fish)
  • Betta fish
  • Apistogramma
  • Angelfish (South America)
  • Firemouth cichlids
  • Rams
  • Corydoras catfish (sterbai cory’s are my favourite) (South America)
  • Loricariidae catfish (suckermouth armoured)
  • Dwarf cichlids (South America)
  • Kuhli loaches
  • Glass catfish
  • Rasbora
  • Congo tetra
  • Hemichromis cichlids
  • Dwarf pufferfish
  • Kribebsus cichlid
  • Uaru
  • Gouramis
  • Discus (South America)
  • Killifish
  • Tetras like neon tetras
You can choose fish like discus or angelfish, dwarf cichlids or small schooling fish like tetras, as well as catfish, plecos, for your aquarium. Fish in acidic conditions shows amazing colors and will behave differently in the aquarium which is more like their natural habitat. Especially if you bought a wild fish. The fish also helps with fertilizing water by their poop and helps the plants by exhaling the carbon dioxide.

It is proved that the humic acids provides benefits to the fish health. They stay in better health and heal quickly while exposed to those beneficial substances. It promotes disease resistance and helps in re-growing damaged fins and skin. It is also proved by a betta fish keepers who condition water with almond leaves. I really recommend Inglorious Betta Youtube channel to all betta fish keepers.

Fish will look more spectacular in the soft water, as it is their natural habitat, and will reveal their best colors.

Aquascaping and setting up the blackwater aquarium

There are different biotopes which you could imitate and aquascape in your aquarium. Some of them are:

  1. Stream with a rapid current and cold well oxygenated water
  2. Marginal area of the certain lake, lots of leaves litter and very low ph
  3. Shallow part of the river with very muddy soil covered with aquatic plants
  4. Sand and stones with higher GH

Every each of those setups will have a different substrate, lighting, water flow and chemical water conditions, as well as, food and fish and plants species.

According to reflecting a natural environment in the biotope aquarium like blackwater aquarium can be separated to 3 criteria:

  1. Geographical aquarium fish and plants belong only to the certain area of the world.
  2. Ecological, all fish and plants live in similar water and environment conditions.
  3. Species related, certain conditions of water that the species need and live in nature without connecting it to the area of origin.

‘An Aquarium is an artificial ecosystem, consisting of biotope (environment) and biocenosis (living organisms). Their selection, combination and compliance to a nature biotope need to be evaluated using the following criteria:’

evaluation criteria for blackwater aquarium


To imitate the blackwater environment you need a botanical materials and specific substrate. You could consider getting special additives specific for the area you are aiming for or making it yourself from half-products such as leaves, twigs, pieces of wood, brushwood etc. There is at least 25 different kind of leaves which you can easily buy in US from the aquarium related website.


Adding a substrate additive works well and mixing those additives with the substrate will function better and be more realistic. Adding certain amount of clay into the substrate and mixing it together to achieve natural proportion occurring in the area which you are trying to replicate. Coconut coir with the substrate will look natural and for sure benefit the whole ecosystem.

coconut coir mulch aquarium substrate


Coco palm bracts will add something special and release even more tannings into the tank

coco palm bracts for biotope aquarium


Different driftwood is also found in the flooded area. The most common pieces of wood to use are: weathered driftwood, redmoor wood, Sumatran driftwood, marsh root, alder wood, apple wood, beech woods (dried and presoaked), birch wood, cherry wood, hawthorn wood, heather wood, oak wood, pear wood, sycamore wood. All the wood needs to be dried out by the sun so it does not have any juice in it. It is always good to presoak the wood and do a bath in bleach solution to remove unwanted hitchhikers, bacteria, fungus or algae.

weathered driftwood for aquarium

manzanita driftwood for blackwater aquarium


various aquarium driftwoodExamples of blackwater aquariums

blackwater discus aquarium blackwater aquarium with cardinal tetras blackwateraquarium tra su forest an giang vietnam 356l blackwater aquarium driftwoodblackwater biotope aquarium rummy nose tetrasblackwater aquarium with angel fishblackwater rio negro shollowsblackwater nature takashi amano


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