Igapó Rio Negro Amazon Biotope Aquarium

Aquatic plants, fish, substrate, and hardscape.

Blackwater Rio Negro Biotope - Benjamin Weidner
Blackwater Rio Negro Biotope – Benjamin Weidner

Technical description:

Blackwater Rio Negro shallow water aquarium biotope.

Tank Dimensions:
 24″ * 12″ * 12″ (l*d*h)


Finnex FugeRay Planted+ Aquarium LED Light Plus Moonlights Tannin stained dark water is not easy for light to penetrate the water column.  To get enough light to grow Cabomba furcata and echinodorus tennellus you will need more lighting for lush growth.

PAR data for a 24″ Planted+ fixture: 3″: 185, 6″: 117, 9″: 88, 12″: 61, 15″: 45


Aqueon Quietflow internal power filter.  Flow rate is adjusted on this one with an adjustment on the outflow at the direction control.  The pump is easy to hide from view and doesn’t overpower the still water species with too much water movement.


Catappa leaves, also known as Indian almond, make great leaf litter for biotopes.
Catappa leaves, also known as Indian almond, make great leaf litter for biotopes.

Most of the igapó areas are simply sand bottom areas with a lot of leaf litter.  There are root systems from trees that are flooded and lots of twigs.  Driftwood can replicate tree root systems but aren’t completely necessary.  Twigs and leaf litter will make a realistic and lifelike representation of the natural biotope without driftwood but its’ addition is also correct and can add to aesthetics in the design of the layout.

 Sand in the Rio Negro is fine in grain and light in color.  A lighter fine grain sand is best.  Play sand will work but natural clean builders sand or river sand will be a good choice if you can find it.

Driftwood: Driftwood that suits your design taste is acceptable.  Leaching tannins isn’t a problem.

Twigs: Small twigs like those from the ends of branches of hardwood trees look great.

Leaf Litter: Finding species-specific leaves is hard.  Oak, beech, catappa, banana leaf, and other similarly available leaf litter will work great.

Water Change:
25 percent water changes by hand each week.

Water Temperature:
FreeSea aquarium heater with LED display.  This heater is small and compact.  Readings are displayed on an LCD in the tank (only in Celcius) and the light might be annoying to some but the heater is small and compact.  Adjusting the temperature is via a panel on the extension cord so you don’t have to get your hands wet.

24-30°C/75-86°F is a general temperature for these fish and plants.  Setting the thermostat on the aquarium heater to 78 is sufficient.

Apistogramma sp.
Apistogramma would make a perfect addition to this small blackwater Rio Negro biotope.  Dwarf cichlids in the Apistogramma selection are many.  Apistogramma diplotaenia and A. regania are good choices for this aquarium type.

Cardinal tetra -Paracheirodon axelrodi
A small group of these would be good in the upper column of the water.  Small schooling fish such as tetras also offer a calming effect for Apistogramma who do better with dither fish as tankmates.

Dicrossus maculatus – Checkerboard cichlid
Checkerboard cichlids get a little too big for a 15-gallon tank and would do better in a 30-gallon aquarium or larger.

Eques Pencilfish – Nannostomus eques
 These pencilfish do better with plants, and floating plants especially.  Leaf litter decomposing can be a food source for pencilfish fry as they develop.  Eques pencilfish prefer low water flow movement as do most other tank inhabitants in this list.

Golden Pencilfish – Nannostomus beckfordi

Glowlight Tetra – Hemigrammus erythrozonus

Gold tetra – Hemmigrammus rodwayi

One-lined Pencilfish – Nannostomus unifasciatus


Saddled Cichlid – Aequidens tetramerus
These need a bit more space than a 15-gallon tank provides.  A 30 gallon or bigger would be better suited for housing these.

Tailspot Tetra – Bryconops sp.


Blackwater biotope aquarium - Photo: Benjamin Weidner
Blackwater biotope aquarium – Photo: Benjamin Weidner

Blackwater biotopes block a lot of light coming into the water column.  Many of these igapó areas don’t have much vegetation growing submerged.  For lower light plants the Finnex FugeRay Planted+ Aquarium LED Light Plus Moonlights will be sufficient but for higher light plants like Cabomba furcata, a stronger light will be needed.  To be most accurate high light plants and lighting can be avoided and plants altogether can be left out of the tank design.  With or without plants the tank will hold its’ own in the wow factor.

Cabomba furcata
Needs high lighting and is more difficult to grow.  These would be better suited for a larger more powerful lighting setup.  It doesn’t help that the blackwater keeps light from penetrating the water column as much as in clear water.

Myriophyllum sp. “green”
Myriophyllum sp. “green” does better with medium lighting and is better suited for the conditions in the tank we set up.  Myriophyllum sp. “green” makes a good background plant and can be used to hide filters and other aquarium equipment.

Echinodorus species
Echinodorus can be used as a focal point in this tank.  Avoid placing it in the very center of the tank to better adhere to the Rule of Thirds and the Golden Ratio.  Larger echinodorus, also known as sword plants, can grow out of the tank for stunning visual effects.  Overhead lighting is needed for this but is worth the extra effort to get it growing.

Echinodorus tenellus
Echinodorus tenellus is a foreground plant best planted sparsely fora realistic effect.  Most igapos areas are sparsely planted.

Azolla species – Floating plants can be used at your preference.  Some fry prefer the hiding area the roots of floating plants provide as they grow.  In many of these kinds of places floating plants are predominanly what will be found if any plants are present.

Fertilization Regimen:

Using self-mixed liquid fertilizer solution by mixing to a solution for 1ml per gallon.

Biotope description:

Flooded blackwater shallows throughout forest areas are common in the Rio Negro region.  This biotope uses blackwater tannins to replicate these natural environments where many small fish suitable for the aquarium live naturally.

Rio Negro Blackwater Igapos Amazon Biotope
Rio Negro Blackwater Igapos Amazon Biotope

These types of habitat are referred to as igapó, a Portuguese word referring to the blackwater-rooted forests.  Found mostly at the lower reaches of rivers and near lakes where slower current is normal, as is seasonal flooding.

Slow moving water doesn’t wash away or carry organic material downriver.  This coupled with overhanging trees or trees growing in flooded areas causes a lot of organic matter to accumulate.  Leaves and twigs sit in the slow water releasing many tannins and lowering the pH of the water naturally.  Even if the tank is not to be planted it will be beneficial to include organic matter in or under the substrate as well as add leaf litter for the comfort and health of the fish.

Organic potting soil can be soaked and rinsed several times to add a layer of organics underneath the substrate.  This adds organic matter for any plants to get nutrients through roots and also leaches nutrients into the water column.  A peat-heavy layer under the sand can also help with lowering the pH and adding tannins to the water.  Leaf litter can be added to the substrate as both a hiding place for fish and to release tannins for the blackwater effect which also has its’ own benefits.

-by Edward Johnson

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