I've done it in the past and currently have some leaves in one of my tanks. You only use the dead leaves, I collect mine in the fall. I just walk around the yard and pick up the nice oak leaves I see and put them in a large ziplock bag. I've never done anything to my leaves, I just take them out of the bags and put a few in the tank. I don't check water stats much anymore, but I doubt they do much. They usually float for a couple days, then they sink. I usually leave mine in the tank until they start breaking up. This usually takes 1 to 2 weeks. Fish, shrimp, and snails don't seem to care about them too much. They get scope them out when I first add them, but once they realize they are not edible they more or less ignore them.
IMO the leaves add a nice natural touch.
