When we talk of anaerobic respiration we are talking about NO3 to N2 conversion. But is this what is really occurring in our tanks when we add a carbon source to it? We know that addition of CS to our tanks result in a bloom of bacterial growth that we can observe in the water column. This water column, which is loaded with oxygen, would and should hinder NO3 to N2 conversion right? So should we surmise that anaerobic respiration occurs in the presence of oxygen, which would argue against proven research? Or maybe propose that anaerobic respiration may not be occurring to the degree thought and definitely not the major player in nitrate reduction.
Another good question, how is PO4 reduced when the nitrogen cycle is independent and does not require phosphate? Anaerobic respiration would not result in phosphate removal as phosphate does not become vaporous like N2. How can these two be linked then with CS dosing? I think the real answer may lie with the word energy. Addition of CS is like giving children sugar. They're already energetic enough but add in some extra sugar and they're running ragged for hours. In theory this energy could be used to be productive. In aquariums we are probably seeing this same effect. With addition of CS, it allows natural processes (bacteria/algae?) to actively utilize and remove NO3 and PO4 from the water column because of their growth and productivity needs. You've given energy to the system and the system is responding by trying to expand to fill its new limits. It pulls in nitrates/phosphates and converts them into an organic form that is beneficial to growth, such as amino acids, phospholipids, etc. These converted forms are no longer detected by test kits and are considered removed. They may stay around in the tank for quite a while in organic form until they are later removed by skimming.
Anyways, that's my thought on it and why I've stated in the past the linkage of nitrates and phosphates. Though the cycles are independent of each other, they work together when looking at the entirety of an organism.
Why do you think your NO3 decline is slower than normal? You may want to explore reduction of ozone input into your skimmer to see if you can increase your skimmer production back to a nominal state. Pushing too much into a small reactor is bad for removal or organics, the reactor itself, and most importantly to you.
