I have a small pond 4'x6'x2' that I've had for about 9 years. I have received pond plants from other people through the years, but I never did think about whether they had leaches or not. When I cleaned little pond last spring, I found several rather large leaches, 3-4 inches long, and some babies. I am building a new, larger pond, 9'x7'x3' . My small pond is overgrown and I'd like to put my excess plants into the larger pond, but I don't want to transfer the leaches and their offspring too. Is there anything to kill them but not harm all the other wildlife? Please help!