Can you have a healthy aquarium where the substrate is covered in leaves? Provided I add them slowly maybe a couple a week and build up? With the target being approx 30% of the tank. I know there was a post recently about gravel vacuuming and I gravel vacuum every week, I guess I won't be able to do this effectively if covered in leaves. I always go out this time of year and collect oak leaves. Last year I added oak leaves and some alder cones. Alder cones looked to produce the most tannins. This year I might boil the alder cones and use the stained water to get the shade of water I'm after. I intermittently use catappa leaves. I don't use them all the time, as it would get expensive, considering you're buying stuff you can go and collect for free when out with the dog. I might just do it anyways. Unless many people tell me this is a terrible idea. I have 7-10 x filtration.