Go back and re-read Tom's TBR on oxygen in the planted aquarium.
Temperature, Altitude, specific gravity, PH all effect o2 levels. Still other events like ammonia, nitrite, and PH effect your livestocks ability to utilize o2. You could have super saturated levels of o2, but if nitrite were to reach toxic levels the hemoglobin would become bound with nitrite, and the fish would still suffocate.
The cooler the water the higher the o2 level, & vice/versa. Plants almost always get enough o2 at night, but if the dissolved oxygen were on the fence, and the tank were well planted, the plants will always get their o2 even if it's at the fishes expense, and fish require much higher levels of o2. So the plants win by default !
Still the fish could survive for quite some time with substandard o2, but you'd eventually notice the stress (Gasping at the surface) up to that point they may very well cope with it but may have a higher occurance of disease, and an increasing mortality rate.
Any of this ringing any bells ???
Many pathogens are commonly present in our aquariums every single day. The breaking point only rears it's ugly head when the fish become stressed.
FTR. Aeration doesn't actually increase the o2 per se. It simply drives off and degasses the Co2. While I'm sure the air pumps are effective, I suspect not adding the Co2 to begin with might be more efficient ?
Better still, shut off the Co2 and run the pumps at night !
If you want to push the Co2 envelope fine ! Just do it in the day time while the plants are hard at work converting it to o2. Co2 rarely kills fish. It's the lack of o2 that trips the scale.
As I said earlier my tanks range from 7.4 to 6.4 ph daily, but my o2 levels are almost always at saturated levels day or night, and my Rainbows are frumping like Bunnies !
How do I do this ? Well ? I shut off the Co2 at night for one thing, but I often use flow rates of 10X to 15X in my systems and the lower flow rates actually have trickle filters with hyperbaric air. My biggest challenges are generally housing/selling all the Cherry Shrimp and Rainbow fry. Supplementing food for my algae eaters, and culling/selling 10 to 15 gals. of plants each week. It's gruelling, I tell ya !