Sorry Brad!
Theo's two rules definitely apply. Create a rough estimate of the species, size, and numbers of your dead fish. Some of the experts on the forum can then tell you if the kill was perhaps due to too many fish above the carrying capacity.
Adding aeration in the future can certainly increase your winter carrying capacity. (And your hottest part of summer capacity.)
Also, remember his Rule #2. Hopefully, you have a significant number of your smaller fish still surviving. Keep sampling your pond this spring and try to determine what you have left, and what you may need to add to have a nice fishing pond again in the not so distant future.
Good luck!
