Aquathol K at 1.9 gals/acre foot (3 ppm) and I'd treat half of the pond (1.5 acres). Treating a smaller area than this will probably result in little to no control and depending on plant density I'd be hesitant to treat more area than that. Treating a band around the pond should control stuff in the nearshore and dispersion should have some impact on the offshore stuff. Probably have to make a second application to pick up what's left. Don't skimp on the rate either. Coontail is a little harder to kill.