Greg, I sympathize with your clients! I think we have too many in our pond. We have NO weeds, 1 acre and 12 carp. Although, I guess the carp need to eat too... They will eat the Purina, just not as voraciously as the Southern States.
We own a piece of another puddle adjoining our property. The fellow that "maintains" it, weed-eats, and the carp devour the clippings that fall into the water. Virtually following him around, In our pond, it is a much more casual approach by the carp. I guess they are just better fed at our place.
Hope the results prove positive for you.