answer:If your planning on doing angels I would personally drain the whole thing and start over. The reason for this being that angels like a much lower pH so it will be much easier to do this from starting fresh than messing about with what you already have. If you had success with the planted tank, I would think tropical fish would be a cake walk for you. And no, you wont have to do much more, maintenance is pretty much exactly the same. If your going to do angels and stuff, why ditch the plants? Ive seen some planted amazon themed angel tanks that looked breath takingly beautiful.