If you've seen the green-to-brown situation before, you may have lost some/most/all of your LMB during one of the previous crashes. Are you certain that such was not the case?
There's no telling what the stuff was from TSC. They used to carry CUTRINE PLUS down here, then switched to a cheaper/inferior algaecide - but "forgot" to reduce their selling price....
Aerators significantly reduce the potential for oxygen problems. However, the operative word is "reduce" - not "prevent". Warm water is less capable of holding dissolved oxygen than cool water. I don't know your water-temps up there, but (inadequately) aerated ponds can suffer from oxygen difficiencies in warm weather when coupled with a catastrophic algae or plant-biomass crash; same as a bank account that has more withdrawals than offsetting deposits.
