I've treated several ponds having duckweed very thick just not in a 50 foot area around the fountain. I have never seen it get rid of duckweed. Also I have been using a herbicide enhancer "growth stimulant" along with Reward. It appears me and the pondowner through about 4 treatemtns have rid of both duckweed and watermeal in two ponds this summer this way. Fo rinfo in one pond... Total herbicide cost of $325 for a 4 acre pond badly covered with watermeal back in APril. Good luck.
