a friend of mine has a small pond, about 1500 sq ' , 3' deep. He wants spray something that will kill the duckweed. I was thinking about an aquatic glyphosate product like Rodeo or Aquaneat. I didn't see "duckweed" on the label. The main problem is that he has horses that drink from the pond and that makes me a little nervous. After reading the label on the product I am still a little confused as to if spraying would be the best choice. Horses have to wait 48 hours before drinking the water??? If this is ok, what is a good aquatic surfactant to use?