Welcome to Pond Boss.
Technically, the grass carp that were stocked should be triploid, or sterile, so they won't reproduce. Good news there is that as grass carp get older, they get more lazy when it comes to eradicating vegetation. So, you may not have as much of a problem there as you think. You can still get rid of each one that's caught, as basis policy.
Electroshocking may be a good way to cull a lot of LMB, but that has a cost.
