Funny enough, oak leaves are in short supply here in San Diego. If I could use palm fronds I would be set though. I have to take a trip to the mountains to find oak leaves. Even when I get them, there's the collecting, washing, boiling, straining, cooling, then finally adding the tannin tea to the tank. Couple hours worth of work. I also do lots of water changes which means any tannins I introduce get diluted fairly quickly. I refuse to do leaf litter for the purpose of cleanliness.