Bobster,
check out copper power chemical, the grape farmers use it here for their ponds and they still have plenty of bass and turtles. I know cause I fish the farm ponds. What the farmers do is put the green power next to the feeding spring and let it slowly trickle into the pond. It takes care of the weed but doesn't seem to affect anything that I know of. You can get it at any of the farm supply stores. The farmers use a very small amount for an acre or more pond. My buddie Garry would use just a handful at most ... Still had some duck weed but very little of the crap.