KC, I don't know if many of your weeds die off over the winter, but if so, 80 grass carp could be a lot.
If you loose a lot of weeds over the winter, then when spring rolls around, the 80 grass carp will be or might be overkill as they should easily be able to stay on top of the weeds.
I know your lake is 10 acres. I put in 15 grass carp in my 6-7 acre lake and they do a good job of keeping my basic pond weed and naiad under control.
I don't know if they are good for milfoil.
If you start with a lesser number of grass carp, you can always add more. On the other hand, they are not so easy to remove if you've got too many.
