1/4 acre pond here.
I'm running 1/4hp rocking piston with one diffuser in the shallow end of my pond, it runs 24/7, it looks just like yours. I also run 1/2hp rocking piston with 3 diffusers in the deeper areas of the pond at night when the air temps are cooler overnight. My pond is long and narrow and a single diffuser running in the center left areas on the ends not covered. I have very green water which makes my pond susceptible to DO sags, current secchi disk reading is 12-13".
I've seen quite a few fish kills, with a DO sag I've noticed that fish like to move shallow, I've seen 16"-17" SMB park their nose as shallow as they can get with their top fins out of the water. I've seen 30-40 15-16" LMB swimming in a school back and forth along the bank in two feet of water ignoring people standing on the bank.
During the summer I will turn the 1/2hp aerator on during the day when we have cloudy rainy weather for an extended period of time.
Watch you water color, if your water goes from very green to brown, you might have a DO sag in process.
