First off, that picture on top is a koi or a goldfish not a grass carp. And they are fine but they will get large and can stir things up but a small pond might only need one or two, I have twenty they are big and you have to get a permit. Aqua shade works well also. For you folks with algae problems, that slimy filamentous stuff that can form great big mats on the surface seemingly overnight. you might try Barley straw. Its very effective.
T