Over time, it will resolve.. The end result may or may not be what you want. One of the biggest factors in stress related events is over crowding. There are certain treatments that "could" be added to the water but it affects every organism in the pond, including beneficials.
You see this in the larger fish but it also affects the youngest as well-but you may never see them or the mortality of.
You CAN help this, even though to a smaller scale, by catching and doing the salt soak as I said above. It'll kill the fungus on every fish you can dip, and the more you can dip before hard winter, the better they will look next spring.
