I wouldn't put any house plant into a tank. Your just asking for trouble. If you want a real planted tank do some research and read up on lighting, ferts, co2 and what each plant type needs are, then go form there. After you have a real PLANTED tank its hard to turn back. Here is a couple pic's of my 125g planted tank.
What are the specs on your 20L? I really like it. I have a 72BF myself and the plants are finally starting to fill in, after a year of playing around with different options, though I recently lost a whole clump of camboba and I cant figure out why. Whats the red plant ?