How to set up an Amazon biotope - with play sand!


Inspired by Heiko Bleher's experiences, George Farmer sets up a planted South American blackwater biotope with some décor already to hand.

In the December 2009 issue of PFK, Heiko Bleher wrote about the habitat of the Rummynose tetra (Hemmigrammus bleheri). My biotope project aquarium is too small for a large shoal of these fish, but I was excited to read that one of my favourite fish inhabits the same location.

I’m talking about the classic Cardinal tetra, (Paracheirodon axelrodi).  There are plenty of other suitable inhabitants too, such as Otocinclus and the Gold tetra (Hemmigrammus rodwayi).

However, I’m a fan of single species set-ups and wanted to keep Cardinals again, but in a more natural setting. Opportunities do not come much better, so I set up my first proper Amazon biotope based on the Rio Negro basin.  


Plants found in this habitat include Cabomba furcata, Cardamine lyrata, Nymphaea species, Utricularia species, smaller Echinodorus species and Azolla species.  

Cabomba furcata or Red Cabomba, as it is commonly known, would make a great background plant with its delicate textures and beautiful colour, so this was a must. Nymphaea and Utricularia either grow too big or are hard to get hold of.  

I thought the popular Echinodorus tenellus would look great as a foreground plant, poking through the leaves between pieces of driftwood.

I didn’t use any floating plants like Azolla, as Red cabomba is light demanding and the tannin-stained blackwater would already limit it.

I sourced suitable driftwood and branches from a local lake.

Sand choice was inexpensive as I had a spare bag of play sand left over the summer in my daughter’s sand pit. Rio Negro sand is very pale and fine, making our play sand the perfect choice. Leaf litter could not realistically replicate those found in the Amazon, so I had to rely on locally sourced oak and copper beech leaves.

I also purchased some Indian almond leaves, widely known to have beneficial properties as well as looking great. I boiled the leaves in a pan of water before adding them to the tank, to ensure they didn’t float when water was added. The boiled water was also added to enhance the blackwater effect. Mixing the leaves added a more complex and natural-looking appearance around the base of the driftwood.


Because I planted this set-up with a couple of relatively demanding species I had to use specialist equipment to ensure the plants grow healthily.

The first consideration is light. The blackwater cuts out a lot of it so I was using two 24w T5 with reflectors to ensure good penetration, especially near the bottom where the E. tenellus lives.

One of the tubes has a pink rendition that brings the red out in the Cardinal tetras and Cabomba very well. With this much light it is important to supply enough CO2 and other nutrients to limit algae. Nutrients are supplied through the Aqua Soil.  CO2 is supplied via a pressurised system attached to a glass ceramic diffuser.  

Water circulation is slow to prevent the Cabomba from being blown about excessively, but there is enough flow to pick up the CO2 micro-bubbles and distribute them around the tank.

The gas bubble rate is relatively low, due to the minimal surface agitation, and the CO2 supply is switched off at night via a solenoid attached to the CO2 regulator.  

The lights are set on a plug-in-timer for ten hours per day. After three days there was noticeable plant growth and, after looking rather sorry for itself after initial planting, the Cabomba reached for the surface.

Water chemistry

The water in the Rio Negro is extremely soft and acidic, with a pH of 4.2-5.5 and conductivity of 7-15.

Temperature ranges from 25-30°C/77-86°F. Replicating the very soft and acidic water would be impractical and unnecessary, as the fish and plants I am using are used to more mineral-rich conditions.

I asked the supplier what water they kept their fish in and matched it with pH 7 and GH 6, but diluting my hard tapwater with the appropriate amount of RO water.

How to set up your Rio Negro tank

1. Choosing the tank

I have used a 60 x 30 x 30cm/24 x 12 x12” (54 l/12 gal) aquarium. My local aquatic outlet ordered me one from the manufacturer and it cost around £25.  It has 6mm regular float glass with clear silicon. There are no braces or rims, so making it ideal to take overtank lighting.

2. Adding the sand

A 25mm layer of play sand is added to the base.  It is almost white and is clean, so does not need rinsing.  It is also inexpensive, costing around £3 for 15kg.  I use around 3kg. The sand is smoothed with a paintbrush and its pale colour is biotope accurate to the Rio Negro basin.

3. Getting the natural look

Driftwood and branches are added on top. Consideration is given to the layout of the pieces to appear natural. The wood was collected from a local lake and cleaned. Later I discover that the wood floats, so I cable tie the pieces together and add a rock to keep it submerged.

4. Introducing Aqua Soil

Aqua Soil is added to the rear, around the base of the pieces of wood.  This acts as an anchor and nutrient source for the plants.  The granular soil is poured into position using a cup for accuracy.  This product lowers the pH and hardness of the water, making it ideal for this biotope.

5. Positioning the leaves

Leaves are added to around the base of the wood. I position the leaves so that they cover the borderline between the sand and the Aqua Soil. I have used Indian almond leaves (Catappa), oak and copper beech leaves.  They are not strictly biotope accurate, but artistic licensing is necessary!

6. Filling with water

The aquarium is filled with water. My tapwater is hard so I have softened it by mixing some RO water. That way it matches that of the fish supplier. I use a colander to carefully and slowly fill the tank with water to ensure it does not excessively disturb the substrate.

7. Planting the aquarium

I let the water settle and become stained with tannins from the leaves for a few days. To enhance the blackwater effect I add some teabags of shredded Indian almond leaves. I then plant the aquarium with Cabomba furcata and Echinodorus tenellus.

8. Caring for the fish

The tank is fishless cycled prior to adding fish. I am using a large external filter, but a small internal is fine.  CO2 injection is also used to promote plant growth, as red Cabomba and E. tenellus can be tricky.  The Cardinal tetras are acclimatised and added – and they feel at home straight away!

The fish

Common name: Cardinal tetra

Scientific name: Paracheirodon axelrodi

Distribution: Rio Negro basins and Upper Orinoco

Temperature: 24-30°C/75-86°F

Diet: Quality dry and frozen foods

Maximum size: 5cm/2”

Swimming area: Midwater

Sexing: Females plumper and larger than males

Breeding: Egg-layer. Difficult in aquarium.  

Biotope on a budget

I’ve used some high-end stuff on this set-up, but it can be replicated at a fraction of the cost. If on a budget, here’s how much you can expect to pay:

Aquarium and lighting: £60

Internal filter: £20

CO2 system: £20

Substrate: £15

Décor and plants: £15

Fish: Expect to pay £2 per fish

Total: £160

This item first appeared in the February 2010 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.