Mike--I'm not sure exactly what leads Ric to his conclusion, but if you for sure had a serious pea-green algae bloom and it is now brown it sounds like the algae all died, which means lack of dissolved oxygen, which would indeed lead to trouble for the fish. So when you say "is this the next stage," the answer may be yes, but maybe not in a good way. If you are able to get started immediately, like tomorrow, with aeration, then go for it; FWIW, I had the tube for my aerator above ground for awhile before I got it trenched in, and merely installing the aerator is a snap--get the stone out to the middle of the pond and plug in the compressor. As far as copper sulfate killing eggs, I don't know the answer; but given the amount of algal growth you've described you would probably want to apply Cutrine or whatever to part of the pond at a time, especially since you already have a heavy load of decaying biologicals underway. You might also consider investing in a round of beneficial microbes to help with consumption of the decaying matter in the water column.
