One thing you can try is a little bit of bleach. Just make sure you rinse really well.
I am in the process of planning a NPT natural planted tank, and it seems like a good option. This is the forum I created, and their is one by Old Fish Lady as well. http://www.bettafish.com/showthread.php?t=98432
She knows alot about these type tanks if it is something you are interested in. If not you will need to cycle and I am not the person to ask about that as I am having difficulty with one of my 10 gallons.