Nitrate reduction and what is aquarium nitrate!

First up what is aquarium water occurring nitrate?
Nitrate is an ion being that it is a charged atom or molecule, it comes in many natural forms and is classed as a salt.
Its make up, unlike nitrite which is one part nitrogen and two parts oxygen, nitrate is of one part nitrogen bound on three sides by three parts oxygen, all called atoms.
Then there is rain water nitrate!
Before nitrate there is an immense amount of naturally occurring and man made ammonia in the air and this atmospheric gas comes down with the rain.
There are other gases in the atmosphere and for nitrate you have oxygen and 78 percent of our atmosphere is nitrogen but due to 3 intense electrons binding this gas, it needs a great deal of abrupt energy like lightning to break that bind so the nitrogen can become a useful protein, so it is in abundance up there.
From being independent atoms these are all able to bind, so along with hydrogen at one atom of atmospheric nitrogen to three of oxygen atoms by lighting, to make nitrate.
In our tanks and in the soil, the nitrogen cycle is the same, bacterial oxidation takes the oxygen out of the bind, allowing the nitrogen to be a pure gas!
All plant life responds to pure nitrogen with increased growth!

What is meant by nitrate reduction?
This is when bacteria or suitable algae up take/absorb this ion, then affectively neutralize the binding charge and use the component they need.
Some synthesis it into a protein or DNA, some algae can fix the nitrogen component, meaning its bind is removed usually leaving only oxygen or with reef aquarium anaerobic bacteria, Pure nitrogen gas.
Cyano bacteria, by using an enzyme called nitrogenaseuses, transforms the nitrogen part of nitrate into more useful bio components in separate cells that do not conflict with photosynthesis in other cells because, when oxygen is present, this action can not happen, from this the oxygen parts of this ion on average are left over.
In diatoms that represent most phytoplankton, the cyano species with in this algae living symbiotically is called Richelia.

It should be known that many microscopic and macroscopic algae such as phytoplankton, corallines, caulerpa and ulva use the nitrogen part of this ion as well and to a degree and rely on some nitrate being present in your reef aquariums waters to survive.

From a natural process called denitrification, anaerobic bacteria that is found in your aquariums waters anoxic zones where oxygen is near to zero, actually provide more nitrogen in the aquarium which can then be classed as eutrophication and can cause possible issues, but with some marine algae, they can also fix-use nitrogen with out light, unlike the others already named here reducing abundant nitrogens impact, so its all good.  
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Nitrate

This particular gas called no3 is near the end of the nitrite cycle and is a mix of two parts oxygen atoms and one part nitrogen atom, the cycle begins with dead tissue, waste and over looked food scraps.

The aerobic comunities in the aquarium converts these varied forms of organic matter via oxidation,which equates to the reduction of the oxygen atom,so ammonia is then oxidized to nitrite,then oxidised to nitrate.

The tank is now left with inorganic nitrate that is a slow process and requires a large area for this extremely slow process of this form of oxygen that is not able to be used by most forms of life but is utilised anaerobic microbes that live in anaerobic-anoxic conditions.
They use the oxygen atoms and leaving only the nitrogen atom as pure nitrogen gas!

What can be used for this very successfully is a substantial oxygen depleted area; some rely on the areas deep with in aquariums live rock, this is not a reliable way if a high volume of waste producers are present.

There can be a fifty percent increase in the volume of nitrate conversion by another form of bacteria by via vodka dosing,which is adding sugars essentialy inspiring the other form of bacteria that can exist in high oxygen levels.

With monitoring,this can be an advantage in a more confined area with out the assistance of extra biological filtration out side of the aquarium.

A particle free low flow to near no oxygen environment is an area that works at best for this process.

It should be rememberd that air born oxygen will adversely affect the anaerobic bacterium as will light while they work on no3(nitrate) leaving only nitrogen(N).

No3 slowly poisons corals and adversely stresses fishes causing partial brown blood disease and abundant adreno gland produced cortisol rendering them weak to parasites and may die like a drug caught fish.

A great number of aquarium fish are thought to have died as a result of being drug caught,they were just in wholesalers or lfs tanks to long with high levels of nitrate.

You can build so many very functional ways in which to seperate the components of nitrate to just nitrogen.

Just pass some of your tank water over something like an under gravel filter substrate,horizontal,vertical it doesn’t matter, just run the water over or passed a clean low to no oxygen area and size does count here.