Steve, I would just use the cutrine granular to knock the nitella/chara back in priority areas (like a beach or shoreline) and leave the rest alone if you can possibly live with it. Regrowth in one month is typical. Aquatic plant control is often like mowing your lawn, you need to repeat after the plants regrow. IMO the low-meadow growth it produces will be preferable to the plant material which replaces it with either grass carp or a pond-wide pesticide application. That is unless your pond is so shallow the nitella approches the surface throughout. In that case you have more of a depth problem than a plant problem. I'm kinda skeptical about being able to manage your grass carp grazing with enough precision to actually pick the percentage of nitella that is removed. If you handle the problem yourself, it will be more work, but you will maintain control over the ponds plant community.

Weedwacker
www.aquaticenhancement.com