From what I have read (I have no experience), the trick for using GC for weed control is starting with few fish and being patient as it can take several years to obtain control. The goal is less than 100% control if you want a pond without problems. That way, fish have plant material to eat longterm. If after 3 years, too many plants are left, more GC can be added. It is certainly easier and quicker to use herbicides, and it is plenty safe if you follow the label. I have curly-leaf pondweed in one of my fish ponds but it has not been a problem yet. If it does get out of hand, I may add a couple GC. I am hoping my emergent plants and ornamental water lilies keep the nutrients at a level that the pondweed stays in check. It does provide winter cover for fry.
