Walnut leaves emit Juglon which is a very efficient stuff impeding other plants to grow below these trees. I once experimented with these leaves in the Paro-aquarium but stopped it because the effect of Juglon on the milieu is not well investigated and may be dangerous.
Catappa leaves do not occur in Paro-biotopes, but they have a mild bacteriocide effect if used in a dried form in the aquarium. Many breeders have a good experience using them. But fresh only; when under water they become older than six or eight weeks they change to a danger with opposite effect. The best thing is to replace them before by a new one.