@AlgaeBarn grew Chaeto under 12 hour and 24 hour period. Chaeto grew more by weight with 12 hour photoperiod.
OK, so I once argued for a light/dark cycle myself, based on nature. But when challenged I researched what little info there is, done some testing myself, & could not come to any absolute conclusion either way, other than this - the light/dark cycle in nature is not a rule, but just one example. If our planet rotated just once on it axis in the same time it takes the Earth to fully travel once around the sun, just as is the relationship between the moon & the Earth, there would still be plants & algae growing on the side of the Earth receiving 24/7 sunlight.
What I learned;
The case for 24/7.
I changed the illumination period from 18 hours a day to 24/7 on my algae scrubber for about a month. The growth was significantly faster & thicker & my NO3 fell from an average of 6ppm to zero.
The ulva stayed the same emerald green color - no brown or dead algae at all - no detrimental effect to the algae in that time period. So the increase in illumination duration correlated with an increase in photosynthesis & assimilation of nutrients.
Depending on the algae species, if there is a constant or near constant supply, even traces of - nitrogen - phosphate - iron- potassium - CO2, I can see no problem with 24/7 lighting. It becomes more a question of what level of NO3 you want to maintain, as light duration will alter this level. Bud Turbo likes the idea of running the illumination 24/7 but at an intensity lower than what would be used for an 18/6 light dark period so constant filtering is occurring but not to the point of reaching zero NO3 in the case of a coral system.
Myself, I would use 24/7 if NO3 rises significantly higher than target level. Then reduce light duration to maintain a specific NO3 level.
I prefer to have the algae scrubber lights out when the tank lights are on so that corals can utilise the available nutrients rather than the filter.
The case against 24/7
I could make the short statement –“24/7 illumination would place a stress on the algae as a dark cycle allows for re-oxidation of the electron transporters of the photosynthetic apparatus.” ???
Or this paper -
Dark respiration in the light and in darkness of three marine macroalgal species’
Dark respiration (non-photorespiratory mitochondrial respiration), which occurs both in the light (RL) and in darkness (RD), is vital for growth and survival of algae and plays a critical role in modulating the carbon balance of individual cells and whole-plants.
Much of the usable energy (ATP), reducing power (e.g. NADPH and NADH) and carbon skeleton intermediates required for biosynthesis and cellular maintenance are generated by dark respiration in a regular manner.
Growth requires a supply of reducing equivalents and carbon skeletons for the biosynthetic reactions, which are produced only by respiration.
3.2 Comparison between RL and RD
The results in present study that dark respiration of the three marine macroalgae, H. fusiformis, G. lemaneiformis and U. lactuca being partially inhibited in the light are in accordance with the findings previously reported in several species of terrestrial counterparts (e.g. Shapiro et al., 2004; Wang et al., 2001; Atkin et al., 2000, 1997; Villar et al., 1994). The percentage of inhibition of respiration in the light at the growth temperature observed in marine macroalgae in this study was similar to the results (28%–53%) found in the terrestrial C3 herbaceous plant, Xanthium strumarium (Shapiro et al., 2004). Our results suggest that compared to RD, RL is a more accurate estimate of nonphotorespiratory carbon loss in marine macroalgae during the light periods, irrespective of the growth CO2 conditions.
