I'm one of those you referred to as having regretted adding grass carp. I hate them. The last time I stocked them was in 1990, so that today they have to be at least 24 years old! I was able to shoot and kill a couple of them, and some died a natural death. But, don't believe the bunk about their lifespans being 15 years! To this day I can't get a plant to grow in my pond! The color of the water in summer time is an ugly, murky green from phytoplankton. Who knows how many GC are still alive? Sometimes I see schools of 8 or more at a time.

For you, maybe just 3 would do the trick, but I wouldn't add anymore than that. Also, I would be patient. The reason I overstocked my pond with GC was I didn't see results quickly enough. When I did see results, it was too late.

Good luck with the curly pond weeds!