David,
If you are concerned about LMB overpopulating, and indeed in most ponds that is exactly what happens, maybe you should consider HSB as a predator. They will be considerably more efficient than CC's, but perhaps not as efficient as LMB at controlling the BG. In the pond that I have HSB, I have the largest BG I have ever seen anywhere.
The HSB will not reproduce, will grow very rapidly, and are great eating and fighting fish. You would need to be careful about having too much overall biomass as time goes forward, but presumably you will be removing the CC's as they mature.
