Starting a new series on step-by-step biotope aquariums, George Farmer creates a Cambodian blackwater pool - and shows how brown can be appealing!
I’ve taken up the challenge of a series on biotope aquariums with mixed emotions. There’s excitement at relishing new projects, but apprehension about stepping out of my comfort zone.
I have always been a fan of biotope set-ups, but felt that many I’ve already seen lacked realism or aesthetic appeal — or both. Heiko Bleher’s recent biotope series in PFK was excellent, but the size of tanks needed made them unattainable for the average reader.
My aim was to create attractive, realistic habitats that are relatively simple to set up and maintain, taking into consideration initial set-up and running costs.
I know more about aquarium plants than fish, so read all I could on my chosen subjects. It has been a huge learning curve, creating the kind of excitement I used to feel when first starting out in the hobby.
I ‘ve started this series with something relative simple that can easily be replicated by most hobbyists, so chose the habitat around some False harlequin rasboras, Trigonostigma espei, I was already keeping.
A search on FishBase gave me most of the information I needed about T. espei. They come from Thailand or Cambodia, inhabiting slow moving or still waters such as ponds, pools, marshes and swamps, often with heavy aquatic plant growth.
I looked at other fish from Cambodia for my 63 l/14 gal aquarium and considered Yasuhikotakia sidthimunki, but these prefer more space than my 60cm/24” tank.
Cross-referencing FishBase gave me a list of 490 species from Cambodia, which I whittled down. I eventually decided on the lovely little Sparkling gourami, Trichopsis pumila.
Blackwater pools typically have a low mineral content, low hardness and pH. Decomposition of organic matter in the slow moving waters results in acidic water, in some regions going down to pH 3!
It is dangerous to attempt to recreate this in an aquarium environment. Instead I chose to use RO water mixed with 20% tapwater. This gives GH 5 and KH 3 suitable for my chosen fish.
The pH started at just over 7, but dropped to just over 6 after a couple of weeks. This was due to the sachets of Indian almond/catappa leaves added to the external filter, as well as the action of granular aquatic soil and oak leaves. The water gradually took on a tannin-stained appearance that added to the authenticity of blackwater.
The temperature is set to 25°C/77°F using a100w heater. Water quality is maintained using an oversized external filter, but with flow control to minimise turbulence.
The Tonlé Sap is a combined lake and river system that changes direction of flow twice a year. It is also the largest freshwater lake in South-East Asia, making it incredibly important, ecologically and financially.
For most of the year the lake is relatively small at around 1m/3.3’ deep, but with an area of 2,700 sq km/787 sq miles. During the monsoon season the Tonlé Sap river that connects the lake with the Mekong river reverses its flow. Water flows from the Mekong into the lake, increasing its area to 16,000 sq km/4,665 sq miles and depth to 9m/30’ deep, flooding fields and forests.
This floodplain provides an ideal breeding ground for aquatic life and makes the Tonlé Sap one of the most productive inland fisheries in the world, supporting over three million people.
In recent years the building of dams in southern China and Laos have threatened the reverse flow into the Tonlé Sap that, in turn, threatens the productivity of the fisheries.
Biotope: Cambodian blackwater pool
Aquarium dimensions: 60 x 30 x 36cm/22 x 12 x 14”; 63 l/14 gal.
Lighting: Any will do on this set-up.
Filtration: I used an external power filter, but an internal will be fine for a tank like this.
Heater: 100w heater thermostat.
Water: 80% RO and 20% tap, GH 5, KH 3, pH 6.0, NO3 <5ppm, 25°C/77°F.
Décor: Driftwood, petrified wood, oak leaves and twigs.
Substrate: Granular aquatic soil and sand.
Fish: False harlequins, Trigonostigma espei and Sparkling gouramis, Trichopsis pumila.
Cost: Expect to pay around £200 for a basic 60cm tank with lighting, heating and filtration, plus the décor and fish you need to reproduce this biotope.
Common names: False harlequin, Lambchop rasbora, Copper harlequin
Scientific name: Trigonostigma espei
Distribution: Cambodia, Thailand
Diet: Flakes, bloodworm and Daphnia
Maximum size: 4cm/1.6”
Swimming area: Midwater
Sexing: Males slimmer and more colourful
Breeding: Egg-layer; requires soft water
Difficulty: Very easy
Stocking: Keep in a group of six or more
Price: From about £1.50 each
Common names: Sparkling gourami, Pygmy gourami, Dwarf croaking gourami
Scientific name: Trichopsis pumila
Distribution: Cambodia, Thailand, Malaysia, Sumatra, Vietnam
Diet: Daphnia, Cyclops and flake
Max size: 4cm/1.6”
Swimming area: Mid-surface
Sexing: Males have longer more pointed anal fins than females
Breeding: Male builds bubblenest under leaf and tries to attract female by flaring fins and swimming back and forth. Female lays eggs, male tends to eggs until they hatch after about 30 hours.
Difficulty: Easy to intermediate.
Stocking: Keep in small groups
Price: From about £2 each
If you can’t find False harlequins in the shops, then the more common Harlequin, T. heteromorpha, or the smaller T. hengeli, will do just as well. Harlequins are found in Thailand while T. hengeli come from Indonesia, so pick any tank mates accordingly.
How to set up your blackwater tank
1 Choose your aquarium
I’ve used a 60cm aquarium. You can use any type, but I’ve used an extra clear, braceless and rimless model. Combined with overtank lighting, the overall look is very effective. This tank has been used for many aquascapes and the clear silicon is becoming stained with algae!
2 Add substrate
I added a granular soil substrate left over from a previous aquascape. Although this substrate system is for planted tanks, it is useful in set-ups requiring soft and acidic water, as it brings down the hardness and pH. However, it clouds easily if disturbed, so add water gently.
3 Add driftwood branches
I have used locally collected wood. It is aquarium safe and I have kept it in my water butt to prevent it drying out. I experimented with positions, using the ‘rule of thirds’ to achieve an effective focal point. The wood protrudes, but this adds to the effect.
4 Add some smaller twigs
The smaller pieces of wood complement the largest ones. Portions are buried in the substrate to help achieve an aged appearance, as if the wood has been in there for many years. The wood is positioned carefully to help maintain a balanced look.
5 Flatten the soil
The soil is flattened with a tool or rake. These are ideal if you want your hands to stay clean. I move the substrate around the tank base to ensure it fills between the pieces of wood. The substrate is deeper towards the rear to help achieve a greater sense of depth.
6 Add petrified wood
Small, relatively flat pieces of petrified wood are added. The colours go well with the remaining décor and fish. Consideration is given to the strata of the petrified wood, ensuring it flows in a natural direction. When viewed together these things matter!
7 Add some dried leaves
Fallen dried oak tree leaves are added. I soaked some in water for three weeks prior and this ensures they sink when added. Although oak trees are not necessarily existent near Cambodian blackwater pools, some artistic license is necessary! Beech leaves also work.
8 Fill it up
Add water slowly. I used a mix of 80:20 RO/tapwater. I used a 6mm airline to siphon the water into the bottom of the tank. The process takes a couple of hours but prevents excessive clouding. The soil is delicate and can easily turn the water into an opaque brown soup.
9 Plug it in
Once you’ve filled up, plug in the equipment and prime the filter. I’ve used a 100w heater and an external power filter with the flow turned down on this tank, but the stocking is low so you could easily get away with just a simple internal power filter to save money.
10 Add the fish
After you’ve cycled your tank (fishlessly, of course) you can add your fish. I’ve gone for a shoal of False harlequin rasboras, Trigonostigma espei and a few Sparkling gouramis, Trichopsis pumila, but you can add many other fish to the same kind of set-up.
This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission. Thanks to Wildwoods’ mail order service for supplying the fish.