The Nitrogen Cycle - It's Important you Know

We've all seen salt water aquariums in books and on the internet as well as in our homes. They come in all sorts of sizes and shapes, some being enormous, then all the way down in size to a nano aquarium. Whatever size they are and whether they are fish only or reef, they rely on nature's life support system, the nitrogen cycle.

Any aquarist needs to basically understand the nitrogen cycle. There is no requirement to become a scientist, just know what is going on. Then the dangers of stressing the aquarium will be better realized (as an example overfeeding, perhaps the main problem with fledgling aquarists?).

All the aquarist needs to do is provide the correct environment for the nitrogen cycle to function. This can be done in several ways that will not be gone into here….except to point out that the nitrogen cycle can reach its full function with some filtration methods and only partially reach it with others. As an example, full function can be reached with 'live' rock and partial function can be reached with a canister filter.

So, how does it work? The following is very simplified.

As part of normal aquarium life, livestock put waste into the seawater. In addition there is breakdown of other items such as algae which has died and similar. On top of that the livestock need food which is provided in the main by the aquarist. All of these will produce ammonia which is toxic. Left unchecked, ammonia will kill our livestock.

Provided a proper environment has been provided, nature comes to the rescue. A colony of bacteria (Nitrosomas) develop and they transform the ammonia into nitrite. The toxic ammonia has been dealt with but it has been converted to another toxin which is nearly as detrimental to livestock. Again, another colony of bacteria (Nitrobacter) transform the nitrite into nitrate. Now we are getting somewhere, nitrate is nowhere near as toxic as nitrite. Depending what they are, generally livestock can stand fairly high but varying concentrations of nitrate.

It is at this point that the nitrogen cycle has gone as far as it can in the example given above, the canister filter. All the bacteria have required is a suitable environment with a good supply of oxygen. The bacteria mentioned above operate in an oxygen rich environment.

If an aquarist with our example, a canister filter, wants to continue and deal with the nitrate, then another filter needs to be set up for this.

The aquarist who has used the other example, 'live' rock, need just let nature continue.

It is in fact best to keep nitrate at low levels, particularly with corals but not exclusively so. The natural nitrate reduction process is known as denitrification. Bacteria once again form a colony, but the environment they need is one very low in oxygen. This is called an anaerobic environment. As oxygen is mainly absent, the bacteria utilise the nitrate. In the process the nitrate is transformed into nitrogen gas. The nitrogen gas is released from the aquarium at the water surface.

There are other ways to remove nitrates (for example algae) but if the full natural cycle can be achieved then this is the best.

As can be seen, our example the canister filter is unable to deal with nitrate as the environment is totally oxygen rich. To deal with nitrate, a further special nitrate filter will need to be employed. Or, if nitrates are not too high, water changes may be sufficient.

'Live' rock (in sufficient quantity, good condition, and with acceptable water circulation) can deal with ammonia, nitrite and nitrate. The bacteria live on and within the rock.

There are filtration methods other than the two examples given. ('Live' rock is however considered to be the best, and can be supplemented by a DSB (deep sand bed)). Whatever the filtration method employed, it must be pointed out that there are limits that any filter can deal with. So don't overfeed. Don't overstock (resist the "one more fish" temptation unless you are sure your stocking level will take it). Also be willing to carry out water quality tests. If the aquarium is new, allow time for the bacteria colonies to build, or for the 'live' rock to settle and 'adjust'.

Next time you sit and view your seawater aquarium, think of the bacteria, nature's engines, working for you.
Peter Cunningham and John Cunningham combined have been keeping salt water aquarium's for nearly 35 years. Visit their site 'Aquarists Online' if you are interested in the saltwater aquarium hobby.