Cocktail anyone?

An odds and ends day of chores, shopping and other tedious things, capped off by logging in to work for a couple of hours to catch up on emails. In the midst of it all decided to do the test trial of the blanket weed remover we bought for our pond. They recommend this glass test to see if it works. However I am not sure what I am looking for. Just looks like pond water with duckweed on top. Might it be working on the blanket weed but not the duckweed?