Hydrated Lime will kill all living things when the pH is raised, and kept, above 11 for a few days. Most plants get killed quickly from the roots and leaves being burned caustically.
If killing duck weed, plants are easy, but the seeds in the bottom muck/soils need to soak in the high pH water, or be removed.
It costs more for the amount of lime needed to raise the pH above 11, but still way cheaper than Sonar.
To kill fish, drain as low as possible, then use what is left in the pond to mix and spray the lime over the entire "full pool" area until all areas have soaked in lime and water flowing back to the water left runs clear.
