I have a pond about 3' wide and about 2 1/2' deep- all fish have died in last 2 months- noticed whitish discoloring on the skin developed then they died. Had about 12 or 14. Would a light in pond help?
A light won't do anything for keeping the fish alive. The whitish discoloration may be parasite infestation if it was noticeable before they died. Otherwise, it may have nothing at all to do with the deaths.
My guess is that there was not enough oxygen in the water to
support that many fish. In fact, I doubt there was enough water unless the fish were very small. If you didn't have filtration, that would be another problem. The light will do nothing at all that I know of.
If you put too many fish in your pond, inevitably, you will have a fish kill. It WILL happen.