SPC I have used Harpoon and Komeen in the past and really liked them. They are copper based products so used at the labelled rates there are no restrictions. They are reasonably priced. If you were wanting to save the American pondered these chemicals may allow you to only kill the coontail. If you have hard water these chemicals won't affect the am pondwees much if you do have low water hardness you could try treating the coontail with the lowest labelled dose and avoid direct contact with the pondweeds. However, if you were looking to kill both tge am pondweeds and coontail I would use Aquathol K.