BJ,
Also re. grass carp, my experience has been that there are very good reasons not to stock them (witness the variety of places where they are illegal). Most relevant here in Ohio, where they are legal, they are very inefficient eaters of algae and very efficient eaters, especially when young, of many ornamentals, lilies, etc. (although happily not water iris).
Grass carp are for eating plants other than algae. A good combination for eating algae are KOI with some Israeli carp. Then to control the off spring of these two fish requires large mouth bass or some similar predator. Natural pond management. Or chemicals.
