When fishes, plants, and food are introduced into the aquarium a process known as nitrification occurs, this is referred to as the nitrogen cycle. This is not unique to aquaria; nitrification will occur in any body of water, or soil, where bacterial action breaks down decaying organic matter and converts it into ammonia. Ammonia compounds are then oxidized into nitrite and nitrates.
These nitrifying bacteria can be termed as beneficial or friendly bacteria, without them aquarium inhabitants could not survive. The process begins with Heterotrophic bacteria consuming fish waste, decaying vegetation, and uneaten food, and converting them into ammonia.
Ammonia/Ammonium:
Ammonia (NH3) is a colourless, pungent, suffocating gas, a compound of nitrogen and hydrogen, and is very soluble in water. The majority of waste produced by fishes is in the form of ammonia, most of which is secreted through the gills. The remainder excreted as faecal matter, is converted to ammonia by Heterotrophic bacteria.
Ammonia is extremely toxic to fishes and must be removed or broken down. Visual signs of fishes succumbing to this toxicity include:
Gasping at the surface Cloudy eyes Frayed fins Listless behaviour Increased mucous production Possible internal and external bleeding (if extreme toxicity exists)
Because of the toxic effects of high levels of ammonia there maybe fatalities, even after ammonia levels are brought under control. Smaller fishes have a higher gill surface area relative to larger fishes; and are therefore more susceptible to ammonia toxicity.
Water changes are the best way to solve ammonia problems. You should do partial water changes over a few days, to bring levels down. Resin-based media or Zeolites are available at aquatic shops and are very useful at removing various substances from fresh water aquariums, including ammonia. Moving fishes to a safe tank will stop the absorption of ammonia immediately, and they can be returned to the main tank when ammonia levels return to zero.
If you have a high pH level, you could try reducing it to nearer 7.0, as this will also reduce the ammonia toxicity.
pH is an important factor in controlling many chemical balances, of which ammonia and ammonium are included. pH is logarithmic, and this is the controlling factor over the presence of ammonia or ammonium. Ammonium (NH4) is less toxic than ammonia, and is formed when ammonia reacts with acids, therefore, if ammonia is present in the aquarium, and the pH of the water is acidic, then ammonia will become ammonium.
As pH rises, so does the toxicity of ammonia, i.e. a pH increase from 7.0 to 8.0 would be a ten-fold increase in the hydroxyl ion, (and decrease in hydrogen concentration) and ultimately a ten-fold increase in ammonia toxicity. It is therefore necessary to test for ammonia before significantly increasing pH.
Nitrite:
Ammonia testing will show a zero reading when the nitrogen cycle is working well, and the Nitrosomonas bacteria are consuming the ammonia and converting it into nitrite. Nitrite (NO2) is also toxic to fishes if it is not removed or converted during the nitrogen cycle into nitrates.
Levels above 1ppm need to be removed by carrying out substantial water changes. This should be done on a daily basis for a number of days, testing regularly, until the nitrite level has reduced to zero. Moving fishes to a safe tank will stop the absorption of nitrites immediately. They can then be returned to your main tank when nitrite readings show zero. Symptoms of nitrite toxicity include:
Listlessness Gasping at the surface Blood and gills turning brown
Nitrite is also dependent on pH, and if pH drops below 6.5, when nitrite is present in the water, the nitrite will convert to nitrous acid. This too, is very toxic to fishes.
Nitrate:
Nitrate (NO3) is the end product of the nitrogen cycle, and is relatively non-toxic; although in high concentrations can still be a problem. Nitrite is converted into nitrate by the bacteria Nitrobacter, and the presence of nitrates in a freshwater aquarium indicates that the nitrification process is working.
Some species are more tolerant than others to nitrate, but a sensible approach would be to keep levels below 50ppm (mg/l). Some of the symptoms of nitrate toxicity would be:
General poor health Poor growth Poor colouring Less tolerance to disease
Nitrates are an essential food source for plants and algae, so if you encourage healthy plant growth in your aquarium, levels will be reduced. Otherwise, if tests show high levels, it would indicate a partial water change is necessary. Regular partial water changes when carried out during maintenance will usually keep it under control anyway.
Ammonia and Nitrite levels will tend to be at their highest in the first 4 to 6 weeks of establishing a new aquarium. This is usually known as new tank syndrome.
Hydrogen Sulphide (H2S) is an extremely poisonous gas that smells like rotten eggs, even in small concentrations it can cause a quick death. It is produced during the decay of organic matter that contains sulphur, and by the action of dilute acid on the sulphides (acid aquariums being at risk).
The usual cause in the aquarium is probably one of neglect, by not keeping the substrate clean of dirt and debris, thereby allowing the decay to build up. An early indication of this problem can be a sudden bloom of algae. The poisonous gas affects fishes by binding the iron of the bloods haemoglobin, which blocks the absorption of oxygen; this causes symptoms, which include:
Respiratory problems Gasping at surface Unusual colouration of the gills
Regular aquarium maintenance, being sure to clean all debris from the substrate, will prevent the problem arising.
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.
Both Kevin Yates & Pbcunningham are contributors for EditorialToday. The above articles have been edited for relevancy and timeliness. All write-ups, reviews, tips and guides published by EditorialToday.com and its partners or affiliates are for informational purposes only. They should not be used for any legal or any other type of advice. We do not endorse any author, contributor, writer or article posted by our team.
Kevin Yates has sinced written about articles on various topics from Interest, Pets and Interest. For more information about freshwater tropical fishkeeping please visit my site at for 30 years or more of. Kevin Yates's top article generates over 12100 views. to your Favourites.
Pbcunningham has sinced written about articles on various topics from Reef Tanks, Pets and Reef Tanks. 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. Pbcunningham's top article generates over 1900 views. to your Favourites.