aquatic weed killer

Are you asking about weeds growing within the pond water itself along the shoreline (emergent aquatic vegetation), or weeds that are actually growing on the bank margin but not in the water per se. It’s always helpful to know what type of weeds you are trying to control, e.g., cattails, etc. before suggesting a specific herbicide.

But in general, the vast majority herbicides, particularly those labeled for aquatic use, when used according to label directions are “safe” (non-toxic) to fish, and certainly safe for air-breathing turtles. Insecticides are totally different ballgame relative to the toxicity question.