Indian almond leaves (IAL) or catappa leaves come from Terminalia catappa, a tree that originates from Asia and Oceania but now grows in tropical and subtropical regions all over the world. Its fruit seeds taste similar to almonds, and its leaves are commonly used in herbal teas and traditional medicines.

When you drop a dried catappa leaf into your aquarium water, the leaf begins to slowly decompose and produce tannins, which are plant-based compounds that gradually lower the pH and stain the water with a yellow-brown tint.

Interestingly, Indian almond leaves are known to have very slight antibacterial and antifungal properties. In nature, tannins help to protect plants from attacks by bacteria, fungus, and other pathogens, and scientists continue to research their antimicrobial efficacy for possible use in human medicine. As the Indian almond leaf soaks in water, microorganisms begin to consume and break it down. They rapidly reproduce and grow into a layer of biofilm and infusoria.

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