Yes, photosynthesis DOES happen at night. Either CO2 or O2 can be both an energy source AND waste product of photosynthesis, AND there are at least 7 KINDS of photosynthesis. and light DOES NOT HAVE to be present for photosynthesis to take place..
"...Photosynthesis is the process where phytoplankton uses sunlight to convert carbon dioxide into food and release oxygen as a by-product. Photosynthesis is driven by sunlight.
Water quality factors like oxygen and pH are regulated by photosynthesis. The greatest concentration of oxygen will occur when the sun is the highest between 2 and 3 p.m. Oxygen will be the lowest right before sunrise. pH will increase-become more basic-as the day progresses and will decrease-become more acidic-throughout the night.
In respiration to convert food to energy, plants use oxygen, and carbon dioxide is released. Respiration and photosynthesis both occur during the day. However, at night only respiration occurs which consumes oxygen. This is what causes oxygen levels to decrease throughout the night. During the daytime even though both reactions are occurring, there is a tendency for a surplus of oxygen to be produced. A cloudy day will be an exemption because there is little to no sunlight.
The pH of pond water is influenced by the amount of carbon dioxide (CO2) present. Carbon dioxide acts like an acid in water. Carbon dioxide is used during photosynthesis. When photosynthesis is not occurring, pH has a tendency to decrease at night When photosynthesis is occurring, pH has a tendency to increase during daylight....