I put about 5 lbs of it about a month ago in my tank and its all gone. And there hasn't been any ducks on it ?????
What have your temps been like? Duckweed dies back around here do to freezing temps. Very little left now and this front hitting now will take care of the rest.
It snowed in 'Nearly Mexico' Texas yesterday. So if the OP is anywhere near me, the answer is 'uncharacteristically cold.'