Honestly, hard to gauge, looks like bacterial or fungal, but how could that happen in air pots?
If you are running daytime 80F 65-75% rh, that hits all the right boxes for VPD if a little on the high side. VPD is meant for transpiration and the movement of water through a plant. There is no transpiration at night; Cellular respiration does not consume moisture from the pot. A high RH overnight cripples gas exchange and cellular respiration.
A plant creates 10% of its energy as ATP during the day, 90% is processed at night. At 80%rh, stomata close entirely, and Cellular respiration will cease.
A higher relative humidity (RH%) indicates a lower concentration of oxygen in the air. This is because water vapor displaces oxygen molecules. Possible there is a slight dead spot in terms of flow at the back of the tank, exacerbating the problem of lack of oxygen.
With the 10°F drop in nighttime temps, the 65-75% rh becomes 75%-85%.
I wouldn't mind knowing your runoff pH. If oxygen is short, this could well be causing anerobic fermentation within your pots as opposed to aerobic, soon as there is a shortage of oxy, acids can skew ph, so let us know the ph!, Hope she bounces back.