I have thought the same, but do not have any real evidence to back it up.
I think that oxygen will dissolve into the water more so during the day time mainly because I think that winds are stronger during the day compared to night. This would yield a better air to water interface. Are these safe statements? If so, aeration would be more efficient during the daytime, but would likely more productive at night due to less wind action and the absence of photosynthesis.
I'm on board WB!
