Grass carp can be dangerous in shallow water if spooked. I have seen adult males knocked out of a boat incurring broken ribs from spooked (by a seine net) airborne carp at 60 lbs. I would not have suggested putting in that many carp. On small ponds it might be easier to drain and scrape out the grasses than catch out lots of big carp. Option would be to drain the pond once the carp have eaten the grass out or rotenone/hydrated lime.