'Blackwater' is the term used to describe the kind of water found in the natural habitat of some acidic water fishes such as bettas, gouramies, killifish and arowanas. The water in such biotopes tend to be amber or tea coloured due to tannins that leach out of driftwood, peat moss and fallen leaves. Indian Almond (Terminalia/Ketapang) trees tend to shed their leaves throughout the year and would even dump almost all their leaves a few times in a year. As a result, where there are Indian Almond Trees, the leaf-litter in the blackwater stream, swamp or pond would comprise mostly of Indian Almond Leaves. In other words, the blackwater is black largely due to the tannins leaching out of dried Indian Almond Leaves that have fallen into the water.

And studies have shown that Indian Almond Leaves leaches not only tannins but many other beneficial substances.

Referring to leaves from the Terminalia catappa tree, Dr Robert J. Goldstein (not the podiatrist- wannabe terrorist of Florida; but the aquarist and environmental consultant of North Carolina who wrote numerous book on fish-keepings), writes in his 2002 paper entitled “Water Conditioners and Additives”:


And he adds:


For this reason, blackwater extract made with Indian Almond Leaves can actually be more effective than those made with peat moss alone.


To brew blackwater extract, follow the following steps:

1.    Collect or purchase a bag of Indian Almond Leaves. If you purchase, Grade C leaves will be good enough, but remind your supplier not to clip off the leaf-stubs if he routinely does so.

2.     Wash the leaves over running water with a stiff brush if they are not already washed. If they are already washed, rinse the leaves.

3.     Get a large pot which is large enough to contain say 2 gallon of water.

4.     Put about 50 (or more) leaves for each gallon of water the pot can contain.

5.     Fill with clean water (preferably with chlorine and chloromine filtered out)

6.     Weigh the leaves down with a chemically inert stone (e.g. granite).  

7.     Let the leaves soak in the pot for a day.

8.     Boil the pot for 15-20 minutes.

9.     Leave it too cool and soak for another day.

10.   Boil one more time for 10-15 minutes.

11.   Leave to cool. The water in the pot should be as black as thick coffee and very fragrant.

12.   Filter the blackwater extract through a coffee paper filter (to trap detritus or any other insoluble matter).

13.   Store the liquid in sturdy plastic or glass bottles.

14.   Refrigerate or keep somewhere cool.
 

Dosage will be 1 ounce for 1 gallon of water in the betta tank. Use your discretion for larger tanks, but do not use more than 1 ounce for 1 gallon of water.

To improve efficiency you may also add anti-chlorine and chloromine into it, but make sure you calculate how much to add so that when you use 1 ounce of your blackwater extract, you will be able to treat 1 gallon of water (to rid it of chlorine and chloromine).

You may also add 6 ounce of aquarium salt to 1 gallon of the blackwater extract. The salt will cause some precipitation in the blackwater extract, but the precipitate will dissolve in water when the extract is added to the tank.

A small amount of salt is not only useful for the fish but acts as a preservative for the blackwater if you intend to store it for longer than a month.