duck weed is the one thing I have always had trouble with... give me a lace leaf or a lily though and I'm in business. I finally got a tank that will support duck weed now though and keep having to rip it out since it is doing so well. At least it is good for spawn tanks! If you have warm water, enough water, and not a lot of water movement it should definitely come back!
Things to keep in mind:
1. Don't dis' germs... they have more culture than most people!
2. You are more likely to find intelligent life in space than on planet earth because that's where everyone seems to be looking for it
3. Even you have photographic memory... it just so happens that you are out of film.