Dark water Aquarium

A Clear View of Blackwater Fish
By Frank Greco, Senior Aquarist, New York Aquarium

When we think of aquariums, we picture tanks of crystal clear water inhabited by brightly colored fishes. However, not all tropical fishes live in such waters. There are those who live in water stained dark by the tannins released by the plant material that falls into their rivers, lakes, ponds, and swamps. These are the fishes of the black waters.

Blackwater fishes are not uncommon in the aquarium trade, although we generally fail to recognize them as such. The very popular neon and cardinal tetras and discus from South America can be considered blackwater fishes, as can the Microrasboras from Asia. Species bettas and licorice gouramies, also from Asia, also live in this type of environment.

Setting up a Black Water Tank

Setting up a tank for blackwater fishes requires no special equipment. In fact, it is set up much in the same way you'd set up any aquarium (see my article, "Building Atlantis From the Ground Up" in the Archives of New York Tails for some basic ideas regarding aquarium setups) with a few conditions taken into consideration:"

• Due to the small size of many of the more commonly available blackwater fishes, especially those from Asia, a larger tank is not a necessity (although a large tank would look spectacular!). Nanotanks and mini-aquariums can house a nice community of backwater fishes.
• Blackwater habitats tend to have soft, acidic water, so you'll need to manipulate both the pH and hardness of your tap water to put in this kind of tank. This is a lot easier than it sounds. There are three ways you can go about making blackwater:
  a.) buy a commercially available blackwater mix;
  b.)boil clean oak leaves (gathered after they have turned brown), and use the resulting liquid (which will be the color of very dark tea), or
  c.) place some long-stemmed sphagnum moss (available from your local garden center) in a nylon bag inside your filter. (You want to use plain sphagnum moss-no additives.)
• A pH range of 6.0 to 6.5 is perfect for these fish, and this can be achieved by mixing some of the blackwater to your tank water, and then checking the pH. You will need to do this several times in order to get within the right pH range.

Still Waters

Since these fish come from relatively slow-moving waters, lots of water movement is not essential (as it would be in a river tank, which will be a topic for another column). Nor do you need a lot of light (a standard fluorescent fixture will do the trick). For decorations, a fine sand substrate and lots of driftwood is the way to go. You can also use boiled oak leaves on top of the sand. Using the boiled oak leaves as part of the decor leads to a more natural looking aquascape, but it also adds to the maintenance load. As the leaves decay, you will need to remove the bits and pieces that tend to fall off. All in all I think it's worth the extra bother. Low-light plants, such as Cryptocorenes, may also be added as part of the scenery, or you may use plastic plants.

Blackwater Fish

There are many blackwater species: Neon and Cardinal Tetras; Chili, Phoenix, Dwarf and Galaxy Rasboras, Licorice and Chocolate Gouramies and Wild Bettas are just some of the types of fish you may consider using for this kind of tank. None of these fish are difficult to feed, and all will accept prepared foods. Your local fish shop should be able to help you pick out others.

The idea of a tank full of tea-colored water may not appeal to everyone, but for those who are looking for something different and exotic, a blackwater tank may be just what you are looking for.