For anyone who can access the original article (I cannot), this article may be of interest to this discussion:
A systematic review and meta-analysis of the direct effects of nutrients on corals
Chronic exposure of coral reefs to elevated nutrient conditions can modify the performance of the coral holobiont and shift the competitive interactio…www.sciencedirect.com
I among these that prefer a NO3 concentration between 2 - 5 mg/L. One of the reasons is that if I read NO3 - I know that I have a N reserve in my water but I´m also run Phosphates well over 0.04 in these cases, There is reports that indicate that NO3 levels around 0.2 mg/L and PO4 below 0.03 can cause P defiency and bleaching among some stony corals. With PO4 above 0.04 - the amount of NO3 is not as critical.
Another reason is the fact as someone state - the only organism I know that really need NO3 is the denitrification bacteria. I prefer to see my aquarium as an ecosystem where bacteria may be the most important inhabitants. In a mature aquarium - there is a lot of different environments with there own set up of bacteria. In the part where oxygen is available - oxygen is used by heterotrophic bacteria in their cellular respiration. But there is also parts that are more or less depleted of oxygen (by the same bacteria) where there is still plenty of organic matter to "eat" Many heterotrophic can in these cases switch from aerobic respiration into anaerobic respiration in order to use the the organic resources. What anaerobic respiration really means? It means that oxygen is not available as an electron acceptor in the respiration - some other molecule must be used. Its here the NO3 molecule comes in as the savior in distress. Many bacteria strains can shift between oxygen and NO3 in the respiration cycle. The oxygen will give more energy but NO3 is first runner up in energy yield. The waste from aerobic respiration is as most of us know CO2 and the waste from anaerobic respiration with help of NO3 is N2 (there is a name for this - denitrification) Its important to note that there is many aerobic bacteria that can switch from using oxygen to be anaerobic - using NO3 in the respiration. OK - i want an anaerobic bacteria population that use NO3 i the respiration - why.
The answer is hidden in the fact the second runner up in the respiration race is bacteria strains that only use sulphate as electron acceptors in the respiration. Our aquariums is rich in sulphates - my own sulphate contend you can see below
This means that if not NO3 is available - the bacteria strains that use Sulphate as electron acceptor will dominate the anaerobic bacteria population totally. - And whats with that?
The most important "what" is the waste they produce - hydrogen sulphide - the rotten egg smell. Its a very toxic compound and IMO one of most common reasons for sudden fish death in mature system. Yes it can be produced even if NO3 is represented but IMO - measurable concentration of NO3 above 2 mg/L limit the hydrogen sulphide producers biomass because the bacteria that denitrify take up rather much of the available area for bacteria growth.
The bacteria that use sulphate in their respiration seems als to be of certain strains that not can use either O2 or NO3 in their respiration.
There is a third reason too - and its about cyanobacteria. My believe is that sometimes is not the mat building cyanobacteria blooms a result of nitrogen starvation but more a result of available phosphorous sources. Many times it had shown up that very low or total zeroed NO3 concertation result in blooming cyanobacteria mats. I´ll think that there is a link between the anaerobic bacteria population between the mats and the substrate. If no NO3 is present - the hydrogen sulphide producers will dominate. Hydrogen sulphide break the bonds between metals and PO4, hence PO4 will be available for consumption. If I got these mats - I always try to stirr the mats in the evening and add NO3 to the water. I´ll think that stirring the mats is good - even if you not suck them out - the mats is not primary the cyanobacteria - they are - IMO - external resources of mainly sugar produced formed during the daily photosynthesis
This was a long post and probably not exactly right in a scientifically way for a microbiologist but an attempt to explain why I prefer NO3 concentrations between 2 - 5 mg/L
And a attempt to explain why I say yes to the initiala question "Do we need Nitrate in a reef tank?"
Sincerely Lasse
No NO3 levels over 0.2 mg/L and PO4 below 0.03 mg/L can cause PO4 starvation and bleaching. As soon as PO4 is over 0.03 - higher NO3 can be tolerated https://www.frontiersin.org/articles/10.3389/fmars.2015.00103/full and https://www.sciencedirect.com/science/article/pii/S0025326X17301601
Yes, as I said it could be true if there is no other nitrogen sources, as it is in the controlled experiment you and others sharing recently. From it: "The ammonium levels found in our mesocosm are very low (< 0.7% of total dissolved inorganic nitrogen) compared to the combined nitrite (~ 10%) and nitrate concentrations (~ 90%). Therefore, the measured NO3− concentrations (combined NO2−/NO3−) represent largely the total dissolved inorganic nitrogen pool that could be accessed by the zooxanthellae in the present experiment."
That is why I've asked if there is positive identification of red slime cyano from reef tanks because I've found some say it is Cylindrospermum (which have heterocysts) and others says Phormidium (which doesn't have) - none of them IMO seems to be the correct identification. 
link.springer.com
academic.oup.com
I've bugged Dan occasionally about how my sand over time shifts from large gains to increasing amounts of fine grained stuff I've called silt.
Similar experiment with detritus buildup in my bare bottom tank
www.reef2reef.com
This is actually a very common observation. People with dinos often report that aminos really increase the bloom. This is a much stronger correlation than zero NO3 connecting to dinos.
Dino outbreaks in hobby seem to have strong correlation to people dropping PO4 to zero (especially with GFO - the correlation might go away if you only look at dropping to zero PO4 by other methods, carbon dosing etc. ) and the correlation to zero NO3 is much smaller.
www.frontiersin.org
Yes, I think it comes from the rocks mostly. All the micro creatures that live in there and digging tunnels or carving the surface are main contributors to this IMO . But precipitation can not be excluded too. I was dosing two parts by the time.
IMO - Here is your explanation why you had more organic detritus than your feeding should cause. IMO - organic carbon is mostly the limited factor for heterotrophic bacteria growth in our aquariums. With adding DOC - as you did - its not limited any longer and bacteria could growth on surplus N and P. Much of your organic detritus ought to be just bacteria mulm.
This effect seems quite solid. And is one area of dinos where the published lit lines up perfectly with what we see in the hobby.
...and of course algae of all sorts can generate particulate organic detritus as it dies or is eaten - the degraded tissue's mass should mostly be from captured CO2. Represents another way to get debris in excess mass of food input.
Agree on that. At least in my case most of the detritus apart of calcium carbonate was actually semi digested algae, it was clearly seen under microscope. Cellulose is hard to digest in aerobic conditions. That’s why I’m having sandbed now and decomposition of cellulose is much faster. my sandshifting goby does great job to burry all the nasty stuff deep enough for anaerobes to take over.
