The point of the thread is that the N you need IS NOT already there. Hence, you add it.
Same thing as carbon dosing, really. We can easily export nutrients by exporting bactiera, plankton, or algae growth. (skimmers, turf scrubbers, macro algae in a refugum, etc). If the ratio of nutrients in our system is not the same as the ratio exported, AND we wish for any of the non-limiting nutrients to be reduced to zero, then we MUST add more of the limiting nutrient, or make a change the the other inputs or exports to/from the system (i.e. food) such tht the limiting nutrient is added in a higher ratio compared to the nutrient we want to reduce further. You are essentially proposing the latter, whcih is fine, though it strikes me as indirect, since you likely will have no hard data to support a specific adjustment (i.e. if you are limited by N being zero and want to reduce P by .05, how much more of a given kind of food do you need to add? Are there even foods that contain an N
ratio that will allow you to make this adjustment?)
The alternative, proposed in this thread, is to simply add the exact amount of the exact nutrient you need. This strikes me as easier, since you can mathematically calculate the amount of a given nutrient you need and figure out excactly how much of a given chemical to dose; and further, there won't be any unintended changes in other nutrients as you WILL get when trying to adjust a single nutrient by adding or removing something that contains ALL nutrients (i.e. food). But, to each his own.
It has now become fairly common for people to add carbon since it limits bacterial growth, which can be easily exported via a skimmer. Adding carbon lets you reduce other nutrients by exporting more bacteria. I would not be surprised if it was soon fairly common to add other nutrients. For example, some people using turf scrubbers for export are finding the scrubber is limited by iron or potassium. These people are directly dosing these specific nutrients in order to remove the limitation and allow the scrubber to remove more N or P. Or, as suggested in this thread, people already dosing carbon may find bacterial growth limited by N. If they're already dosing carbon, dosing N too isn't really a quantum leap.
It seems that part of your objection is your view that nitrogen is a "pollutant" in our tanks. While it certainly can be, that is a narrow view compared to it's larger role. Granted, it is a view that the hobby has about many nutrients - but sometimes advancements in a hobby require a change or broadening of the point of view. Take planted freshwater aquariums as an example. It is fairly common in that niche hobby to dose a wide range of nutrients (nitrogen, potassium, carbon, phosphate). Sure, these things may all technically be "pollutants" in the sense that they CAN contribute to poor health in the livestock, but dosing them in an intelligent manner can clearly lead to improvements in the overall environment in the aquarium. If the planted freshwater community refused to see them as anything except "pollutants" then the hobby would never have reached the point it is at today.
