I usually change my leaves when they start feeling really slimey. I don't see why you couldn't use your own banana leaves, as long as you are sure that they're not covered in any fertilizer, pesticides, etc, and that the plant you have is the right species. I see them packaged for this purpose all the time, and they're supposedly ideal for healing: http://www.drak.de/en/products/natur...na-leaves.html
I tried soaking the live oak leaves for a few days, and they havn't really changed the water color any. I thought it was supposed to darken the water at least a bit? Maybe live oak leaves won't work, they're much stiffer and thicker than regular oak leaves.