Six Mosquito Dunks to a package are enough to keep the garden and yard mosquito free for months. Each dunk releases an effective larvicide (Bt Israiliensis) into standing water for up to 30 days, treating up to 100 sq ft of surface water regardless of depth. Mosquito Dunks kill mosquitoes before they get old enough to bite and are used to treat stagnant water in birdbaths, flowerpots, rain barrels, gutters, and unused swimming pools and hot tubs. Disks can easily be broken into smaller pieces or anchored to avoid being washed away.