they are infact almond leaves. The procedure for introducing black water in your arowana tank is as follows
!) Remove only only dying leaves from the tree, no green leaves please.
2) Keep the dead leaves in the sun for a min of 2 to 3 days so that they are brown
3) Keep the brown leaves in a bucket of water for a day or two
4) you wouold find that all the tannins from the leaves are mixed with water and the water has turned brown
5) now put the water in your tank