At what time of day is the pH in a waste pond typically the lowest?

The pH in a wastewater pond is typically lowest at sunrise due to the natural processes occurring overnight. During the night, photosynthesis in aquatic plants and algae ceases, leading to a drop in oxygen levels. This reduction in oxygen inhibits the breakdown of organic matter, resulting in the accumulation of carbon dioxide, which can combine with water to form carbonic acid. This increase in acidity causes the pH level to decrease.

As the sun rises, photosynthesis begins again, helping to increase oxygen production and subsequently stabilizing or increasing pH levels throughout the day. Thus, the timing of these natural processes makes sunrise the time when pH levels are generally at their lowest in a waste pond.