That big of a pond makes it real tough. More like a small lake. Many here know I am not a big fan of grass carp. And you illustrate why, in the real world. Sometimes they are just not that effective. You never know what they are going to control, kind of control or just ignore. If you are down in Texas, I might have gone with Tilipia instead. They are eating machines. But to be honest with that heavy of an infestation expecting the carp to get a handle on it might be a bit much. I am assuming you got triploids which are never going to reproduce. With Tilipia they will populate as long as there is something to eat, and they are prolific. And they will eventually get ahead of it. With Carp it is more or less time will tell.
I had a smaller pond a little over 5 acres with a 99% infestation. I did a combination of herbicide, then manual rake, then herbicide. Just ran out of options. Now I have less than 1%. I used no biological control fish. But Tilipia die off here, and you are permitted to death getting Grass Carp in here. We do have hybrid carp that can't reproduce, but again, they have thier own menu. My worst weeds are Eur Milfoil and Coontail. They are just pond killers. I'd herbicide it just to give the Carp a chance to get on top of it and let them grow needing to control not as much vegetation. Good luck to you.
