I'd pick up an anubias nana (also called dwarf anubias), and see if you can get some duckweed. The anubias will be the long term plant. You can attach it to a rock or wood, where it will be very happy, or you can plant it like a conventional plant. I've had great luck with them on rocks and wood. While it is getting established, the duck weed will soak up nutrients and multiply like mad. Scoop it out and throw it away--this exports the excesses completely out of the system. Petsmart around here usually has nice plant tanks--no fish, which means they won't introduce a disease. I still would clean it--use a 1:10 bleach water solution. Submerge the plant for a count of 30, rinse well in de-chlorinated water (water from a recent change is ideal!).