Do algae need a dark period?
This is a very relevant question since it can affect macroalgae growth. I remember from my high school biology lessons that plants need a dark period for growth.
Trying not to get too technical, Light reactions need light to produce organic energy molecules (ATP and NADPH).
Dark reactions make use of these organic energy molecules (ATP and NADPH). This reaction cycle is also called Calvin Cycle. ATP provides the energy, while NADPH provides the electrons required to fix the CO2(carbon dioxide) into carbohydrates.
Although algae are not plants, the phosynthetic process in them is the same, so it appears that algae do need a dark period for building their cells.
I leave my ATS lights on 18 hours a day (Floyd in the threads on algae scrubbers recommends keeping the lights on for 18 hours). and my fuge lights on for 8 hours. I have found that the chaeto under my ATS lighting grows much better than the chaeto in my fuge which makes sense. I can always increase the photo period in my fuge depending on how much I want to reduce PO4 and how fast.