I've seen grass carp completely bypass American Pond weed for hydrilla. Out in California they are mainly used in canals or moving water. Plus they are a pain just to get into the state. Very expensive also. I'd never put them in for pondweed. I'd mechanical harvest the weeds I wanted thinned out or gone. Is it the grass carps favorite food? No. They will look for other submerged plants first.
Maybe it is different in Ohio, but I'd check if you must stock triploids, need a permit or written authorization. Then do a cost analysis. One other oops consideration, after they eat everything there is to eat, and completely knock the vegatative balance out of whack, can you deal with algae blooms? They won't.
