Duckweed is a floating plant that really only requires the right light. In lower light it won't do well, but in medium-high it will multiply fast.
The only form of payment I'll take is paypal. My address is cajunfiberco @ gmail.com (w/o spaces)
If it multiplies in your tank too fast, like it does in mine lol, you can just scoop out a bunch with a net and throw it in the garbage. That's what I was doing until duh, realized I could sell it ;)