Also without knowing the exact size of your pond, you said that nearly 100 lbs of fish were killed off. Simply having too many lbs of fish biomass per acre in a pond will lead to fish kills during that "15" minute timespan where pretty much I would have to agree that a combination of many factors came into play here.
Also keep in mind that even if you havent had a problem with your pond before, that it is aging, and nutrient loading, and basically filling in every day since it was born. There are steps mentioned above to take that can essentially reverse the effects of aging, and also increase the natural carrying capacity and dissolved oxygen levels throughout your pond.
