Yea, you could also add sugar as a reduced carbon source, but why is a reef tank so carbon limited for the bacteria to start with?
The type of carbon is important here. Organic reduced carbon or DIC: CO2/HCO3/CO3?
They are very different and play very different roles.
Unlike reefs, we are supplying DIC mostly in the CO2 form for plants which use that as a carbon source and take DIC=> organic reduced(sugars basically) carbon.
In reefs, corals, shellfish, marine plants that form CaCO3 take DIC and form CaCO3, not....organic reduced forms of carbon.
Some/most macro and micro algae, all plants can take HCO3 or CO2, none of which are really limiting in oceans, and use it for reduced carbon sugars.
Perhaps it would be wiser to have a Refugium to supply the organic carbon?
Carbon will leach out of these plants/algae and supply the bacteria with a source for further NO3=> N2 gas, or better yet, use plants/macro algae to directly remove both NH3 and NO3
Refugiums also work with stunning success in reefs also.
Try feeding the bacteria to you tangs, I can do this with the macro algae/plants.
ETOH is not the only source of carbon that can be used in a reef, there are many far less $ sources. Perhaps you do not want to add refugiums.
So adding a source of reduced carbon is for the bacteria really, since reef folks try and run their tanks so lean ande do not feed their fish much or have hardly any fish.
The bacteria that denitrify become Carbon limited basically.
This can happen in FW tanks also, but if you have a fair amount of plants? Never.
But we add NO3/NH4 etc, marine planted tanks also do better dosed with some KNO3 etc, since the sexual induction is general caused by a reduced limitation of NO3, then they melt(Caulperas mostly). If you keep the NO3 at 5-10ppm, they do not. I add about 0.2ppm 1-2x a week also to keep the NO3 uptake steady and not limited by PO4 also.
This like the booze/reduced carbon addition, increases and helps the NO3 uptake.
Bacteria, plants, coral, fish etc, all can have a limiting nutrient/food, and by reducing one, you limit the others.
So if you provide that limiting factor, say reduced Carbon, this allows the other nutrients to be metabolized.
If you strongly limit PO4 in a planted tank, the demand for CO2 goes way down, 2-4-10X depending on how limiting, and the rates of growth also are greatly reduced proportionally.
See Liebig's law of the Minimum and then add carbon(organic and DIC) to that concept.