Just another thought. If a plant takes over your pond after several years, it doesn't always require chemicals to eliminate it or control it. Grass carp in high numbers did a complete clean out of submerged plants in my pond that was chocked with the dreaded Eurasian Milfoil and it never came back. Had I wanted EM but controlled I would have used lesser numbers of GC. GC won't always eat the plants you want eliminated or controlled but in the numbers I used, 18/acre they cleaned out everything. The Curly Leaf Pondweed I like is curtailed further with a few GC besides it's natural ability to thin out in the heat of the summer.
