[Subsea]

Nutrients are uptaken during lights out by both bacteria and filter feeders. When I use night vision to peak into my tanks, I see many more fans, feathers and tentacles.

You are right about lights out in a reef tank. Oxygen becomes a critical issue for fish first. Bacteria consume massive amounts of oxygen. In my case with a 6” Jaubert Plenum across the footprint of 1.5’ by 4’. At three cubic feet of substrate that is 25G in a 75G tank. That is a lot of surface area for bacteria. Bacteria are the biggest player in my tank and I say in everyone’s tank. Consider this, bacteria consume nutrients and in so doing, they become food for everybody else in the tank either directly or by feeding an organism that becomes food, particularly in the case of filter feeders, which includes corals.

Let us get in depth about pH fluctuations in a reef tank. I say, much fuss over nothing. The pH fluctuates on the reefs of the ocean. Steady state pH is not normal. Is it harmful, I don't know. Six months ago, I schcronized my display tank and refugium light cycles. I was not concerned about oxygen depletion because of surface skimmer with agressive circulation at the surface. When surface water is skimmed from display, it cascades over bioballs in first chamber of mud/ macro refugium. Some of the most important chemistry and physics in our reef tanks take place at the water air interface. Due to Dynamic Equilibrium between the partial pressure of the gases: nitrogen, oxygen and carbon dioxide are allowed to exchange back and forth between free gas in air and a saturated gas in water. How does that help our reef tank? Excess carbon dioxide is released to athmosphere thereby stabilizing pH in the water. Oxygen enters the water as demanded by the “partial pressure law” for gases, this is dynamic equilibrium of oxygen without photosynthesis.

I saved nitrogen for a seperate paragraph because of its complexity with bacteria. Cynobacteria, without them our athmosphere would be methane and sulfur. In a process called “nitrogen fixation” bacteria convert free nitrogen gas into an inorganic nitrate molecule, which is food to the entire reef community. In the marine environment, this is done with cynobacteria. On the opposite end of the spectrum in a reducing environment of oxygen, facultative bacteria consume an oxygen molecule of nitrate and release a free nitrogen gas molecule.

What I have described is the tip of the iceberg in natural reefkeeping. I call it “Intelligent Design”, which is above my pay grade.