You might also hear Indian almond leaf shortened to IAL or referred to as catappa leaves, named after the tree it comes from. IALs are believed to aid the fish in a number of ways, they increase fertility, health, and vigour. Reduce Ph in water, aid in the recovery of diseased or damaged fish and the tannin quickly colors the water.
It is believed the tannins released by Indian almond leaves kill bacteria, fungus and viruses, allowing an injured fish to heal much quicker.
It is even suggested that Indian almond leaf might be a better solution than antibiotics and other medications when fighting bacteria and fungus in commercial fish farms.