Cokeman,
I'm thinking that the main culprit was too many fish. 700 10-12" channel catfish is a lot of oxygen demand. Given that your algae treatment was 8 weeks ago, the copper should have been long gone. Even though you suppressed new planktonic algae growth with dyes (and therefore oxygen production), you were playing with fire by having so many catfish that you were feeding. Although windmill aeration is not the best solution, you got some benefits, but it just prolonged the ineveitable.
It's easy to get gung-ho with a pond and stock fish at rates that approximate what could be found in hatchery grow-out ponds. Hatcheries, however, often have fresh water pumped through routinely or have high oxygen surface agitators.
When you push the envelope with too many fish, bad things can happen. Sure, killing too many plants at once can cause oxygen squeezes, but you were 8 weeks post treatment. My advice is to saddle-up again but reduce the amount of catfish you stock and come up with a feeding regime that is safe. As you know, fish are like us in terms of cellular respiration. The more you feed, the faster they grow and metabolic rates increase. This all requires oxygen.
Good luck.
