What you need is some sort of emergency aeration. How about turning it off, switch over to a sump pump to and spray the water back into the pond allowing it to degas and absorb oxygen.
If not that, then turn off one of the diffusers and bring the other one to the 4 foot depth to circulate the upper already aerated water.
My experience has shown that if an end user actually flipped the pond over without doing a complete start up, then all the fish turn up within 24 hours and not just 20 fish of one species.
