I obviously am not saying that GC have no use in pond management, given the fact that three of my ponds have been stocked with them. I'm just concerned with the misconception that GC are a inexhaustable nutrient sink. The math is really simple and indisputable. The dry weight of your grass carp mass increase will be about what your plant weight dry decrease is. You can't make something from nothing...or nothing from something for that matter. If your twenty grass carp have a net annual weight increase of sixty pounds, and the fish are comprised of 75% water, then you have only "created" 15 pounds of mass from the nutrients digested from plant life. Try to explain to me how you can lose any more than 15 pounds of dry plant weight in the process. One exception to this rule is in ponds with good flow-through. If the plant biomass is occupied in smaller organisms, like single-celled algae then your pond is more likely to see a net decrease in biomass in a rain event by allowing nutrients to be ejected through your overflow.
