What are they?
Scientific Name: Terminalia catappa
Common Names: Ketapang (Indonesian), Bengal almond, Singapore almond, Ebelebo, Malabar almond, Indian almond, Tropical almond, Sea almond, Beach Almond, Talisay tree, Umbrella tree, Abrofo Nkatie (Ghana), Tavola (Fiji), "Castanhola" (Northeastern Brazil), Zanmande (creole) and kotÅl*
Source: http://en.wikipedia.org/wiki/Terminalia_catappa
As well as lowering the pH and removing some toxins from the water, they also act as a food source for some shrimp.
How to prepare:
The dry leaves should be stored in a cool and dry location. When ready to use, wash and put into the tank. You can either weigh it down with a rock or let it sink which usually happens after 24-48 hours.