I am waiting to see if I actually have a weed problem in my new pond. One never developed in my old pond (10 years old). and I don't want them to eat everything green. I want to keep my ornimental water lilies and some submerged vegetation for cover. If things start to get more weedy than I like, I'll start with just one or two GC and give it a couple years. I can always add more, but I am pretty patient. I am giving my forage 2 years before adding preditors.