I get emails with questions. I try to answer the best I can. This is an example:
My next door neighbor had a mosquito killing mister sort of system installed that sprays ULD HydroPy-300 two times in the am and two in the pm.
Within days our gold fish began dying. Our water tested great for fish conditions. I couldn't find anyone local to test the water for pesticides. There is approx. 80ft w/some trees between their system and our fish pond. I did take note that we lost more fish after a couple of particular windy days.
Do you think their system is what is killing our fish? The company that installed the system said there is no way their system had anything to do with the fish dying. However, the neighbor agreed to cut off the system for a few days and the fish stopped dying.
I would bet the ranch that the mister killed your fish.
I don't know the pesticide they used in the mister. Do you have a local cooperative extension or local agricultural college in driving distance? Is there a private lab
in town? Anytime there is spraying done, the pond needs to be covered. This can happen when gardeners use pesticide sprays, when grass cutters are there. Even when you or a neighbor is sanding a house prepping it for a new paint job, do at least a 50% water change just for safety's sake.