Hey, so I was reading something about having a split up time frame on lights being on/off. Cant recall the exact term, but the jist of it is that you have lights on 4 hours, off 3 hours, then back on 4 hours, then off. Granted, I understand this is not optimal for bulb life, but then again, they are cheap enough to replace anyways. Any thoughts on that?
This is usually termed the siesta method. It is actually connected to CO2, but some background wil help in case this is new to you.
Plants will photosynthesize if light is sufficient intensity, and provided all 17 required nutrients are present. As soon as one of these is no longer sufficient to balance the rest, photosynthesis slows, and may even stop altogether, depending. It is at this point obviously that algae begins to take advantage. [For this discussion, we are assuming the light intensity is basically what is needed; more than this will cause algae regardless.] In the low-tech or natural method planted tank, CO2 is the nutrient that usually runs out first, since we are relying on the naturally-occurring CO2 whereas we can add other nutrients artificially.
Plants photosynthesize full out if everything is present. As CO2 is a macro-nutrient, it gets used up fairly quickly, and faster than it can be replaced during the period of brightest light. Remember that most of the CO2 comes from the breakdown of organics in the substrate; that resulting from the respiration of fish, plants and bacteria is much less in quantity and insufficient on its own--and yes, plants respirate just as fish do, taking in oxygen and giving off CO2, day and night. It is only during the day under sufficient light that they also take in CO2 and give off oxygen in greater amounts than the respiration reverse. The production of CO2 in the substrate occurs continually, but during the night when the plants are not taking it up, it multiplies to a much higher level. When the light comes on, photosynthesis begins to use this CO2, and at some point the CO2 becomes depleted. The time this takes depends upon the level of CO2 produced during darkness, the number and type of plants, and the fish load.
The principle behind the siesta method is that the period of darkness for a few hours between two periods of light allows the CO2 to rebuild.
The problem is that plants and fish do not appreciate this arrangement. Fish, like all animals, have a circadian rhythm, an internal "clock" that regulates their system, and is dependent upon light/dark. It is intended to run over a 24-hour period. Ironically, plants have a similar feature that can distinguish the duration of light, though the upsetting for plants appears to be less of an issue. It takes fish a period of time to adjust to daylight and darkness, roughly around 30 minutes, and when the expected day/night cycle is interrupted and in effect doubled, the fish's physiology has no option but to react. The fish may undergo stress, which weakens the immune system and leads to various other issues.
The light over a fish tank has a very significant effect upon the fish, much more than most realize. I won't go into this now, but if asked I can; I have touched on this in other threads in the past few weeks.
Byron.