My internal dialog can imagine my biologist wife yelling at you already.
Honestly i do not know the full scope of this one, but if there's one thing I've learnt from observing her work over the last decade...it's humans need to stop adding chemicals to water bodies with the goal of thinking they're helping something.
Mosquito dunk is some kind of microbial culture that’s supposed to be safe.
Note it's not a chemical agent; its bacterial spores that infect and kill mosquito larvae! I'm pretty sure they're not harmful to anything that isn't a mosquito, blackfly, gnat, or midge. Though midges are important to pond ecosystems as a source of food for fish and dragonflies and stuff? Idunno, ask this guy's wife.