Catappa Leaves, also known as Indian Almond Leaves or Terminalia Catappa Leaves, is the leaf from a large tropical tree in the Leadwood tree family. It is considered native to tropical Asia & northern Australia, but is today also common in tropical parts of the Americas.

Catappa leaves have been a long kept secret of breeders of Bettas Splendens (Siamese Fighting Fish) in South East Asia. It was long ago noticed that fish that lived in the waters next to any of these trees ( the leaves of which would fall naturally into the waters ) were found to be healthier and more vibrant than their counterparts. It was surmised that if one were to introduce the leaves into aquariums one could achieve similar conditions as found in the fishes natural enviroment. The leaves were found to help keep their fish healthy with strong anti-bacterial properties and promote better breeding.

When the dried leaves fall into the waters it will leach a strong brown dye that is full of organic acids like  tannic acids, which gradually turns the water into red-brown like tea and effectively reduces the ph levels in water, releasing it's rich organic compounds such as humic acids, flavanoids (quercetin and kamferol) and tannins (s. a. punicalin, punicalagin and tercatein) into the water which absorb harmful chemicals. other fish known to benefit from indian almond leaf use include baby discus, dwarf chiclids, killi fish, rasboras, catfish and black water tetras. tannins, by the way are described by horvath (1981) as "any phenolic compound of sufficiently high molecular weight containing sufficiant hydroxyls and other suitable groups (ie carboxyls) to form effectively strong complexes with protein & other macromolecules under the particular enviromental conditions being studied."

From an article by Mr. Chris Yew (www.siamsbestbettas.com)
" What is Humic Acid ? Is it a mixture of several organic acids ? "

Humic acids are a complex mixture of partially decomposed and otherwise transformed organic materials. The freshwater humic acids can come from a variety of sources, most of which are on land (decomposing terrestrial vegetation.) These substances wash into lakes and rivers, undergoing further transformations along the way, and ultimately into the ocean.

Humic acid contains Sulfur, Nitrogen and Phosphorus in varying amounts. It also contains metals such as Ca, Mg, Cu, Zn etc. which can be 'chelated' in some undefined way. Humic acid can be broken down into two groups based on the polarity and size of the individual 'compounds'. The smaller, more polar fraction is generally termed fulvic acid and the larger, more non-polar fraction is generally termed humic acid. Humic acids are the end product of microbial degradation of plant and animal debris and are one of the most important constituents of fertile soils. Tannins, lignins and fulvic acids are sub classes of humic acids. They all tint the water yellow.

Tannic and humic acids may be useful for inhibiting many types of bacteria including cyano-bacteria & are fairly benign for your fish. Another paradoxical effect of humic acids is the detoxification of heavy metals. Humic material and detritus in the aquarium also rapidly absorb and detoxify many chemicals including zinc, aluminum and copper! One might expect them to be made more, not less toxic by humic acids, but the studies seem to indicate a detoxifying effect.

Also important to know: The harder the water the more ineffective the humic acids - - - more exactly: the dissolved lime in the water produces undissolvable calcium humates. So, the higher the water hardness, the higher must be the supply of humates in order to achieve an acidifying effect. The softer the water, the less humates are needed and the better the effect. It creates a natural environment similar to that of the lakes in the tropical rainforest and some area of the Amazon River. It also induces spawning for most soft water and acid loving fishes".