Grass carp for duckweed control

We've got a duckweed problem! So we're going to buy some triploid (sterile) grass carp to help get the duckweed under control in our pond.
The rule of thumb is to use 10 grass carp per acre of pond for general maintenance. Ours is about 2/3 acre so we're going to buy 7 of them and see if they help.
Hope these little fish are hungry!