I tried using grass carp and even had them in the pond to begin with as the coontail first started taking hold. I'd add more grass carp and it never seemed to help get things under control. A couple different times an otter would get into the pond and maybe they ate or killed the grass carp. When we finally drained and dug out the pond two years ago, I didn't see a single grass carp or fish of any size flush out or be left on the bottom. I only saw tons of small fish in the fields below us.
That stuff ruined my pond and I imagine it played a big part in a massive fish kill we had about 8 years before we drained it.
