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Friday, October 05, 2007

The role of nitrates in a sal****er aquarium
By ???-????



Over the years, I've found a great amount of information regarding the role
that nitrates (NO3-) play in sal****er systems. The majority of the
information available tends to be confusing and inconclusive with respects
to the level of danger this compound represents to a healthy sal****er
aquarium. Much of this information characterize nitrates as a toxic,
unwanted and dangerous compound that should be brought down to zero in most
cases and recommends to the fact that "high" levels of nitrates are
extremely dangerous to the fish. While I agree with this basic assumption,
the information that follows will clarify some facts regarding this compound
and represents it as an unwanted byproduct of a healthy system that should
be kept to a minimum but should not be a catalyst of drastic actions.



Where do nitrates come from?



Nitrogen enters your system in one of two ways. The first and most
important is in the form of food you give to your fish. The second and
extremely less important is by gaseous exchange between water and air. The
latter is very hard to achieve and could be considered negligible to our
analysis.



Once your fish ingests food, it utilizes its nutrients for metabolic
processes, to increase or replace body mass and/or to store as fat for later
use. The amount of nitrogen that is not employed for either of these
purposes is excreted back to the system.



By the time the organism's metabolism is done with the food, most of the
nitrogen had been transformed to ammonia (NH3). In the form of waste is how
we see the majority of the nitrogen thrown into your system together with
other compounds like phosphates. At this point, a process known as
nitrification starts transforming the now very toxic ammonia to other forms
of nitrogen compounds.



A group of bacteria known as nitrifying bacteria is responsible for these
transformations. The first group of these bacteria is known as nitrosifyers
(ammonia-oxidizing bacteria). These bacteria transform ammonia into
nitrites (NO2-) as follows;



NH3 + O2 + 2e- + 2H+ ? NH2OH + H2O

NH2OH + H2O + 1/2 O2 ? NO2- +2 H2O + H+



Nitrites are still a very toxic compound and can cause serious damage to
your system. Once there is enough nitrite to work on, a second group of
bacteria called nitrifying bacteria (nitrite-oxidizing, nitrate producing
bacteria) enters the now advanced nitrogen "cycle" and oxidizes even further
the nitrites turning them to nitrates as follows;



NO2- + 1/2 O2 ? NO3-



Once the nitrogen cycle has changed nitrites to nitrates it enters the food
chain. The nitrates are very useful compounds for plants. It is here that
the Nitrogen Cycle fails in the aquarium. Nitrates are supposed to be
absorbed by plants and turned into animal matter by herbivores which in turn
get utilized by carnivores completing the food chain and starting the cycle
ones again.



If there isn't a complete food chain in a system, the nitrogen cycle turns
from a cycle to a "one way highway". In other words, food is turned to
ammonia by your fish; ammonia is then turned to nitrites by the nitrosifyers
which are turned to nitrates by the nitrifyers. The end result is lots of
nitrates.



Are high amounts of nitrates a sign that the nitrogen "cycle" isn't working?



The answer to this question is no if; the levels of ammonia and nitrites are
at or near zero. What this mean is that your nitrifying bacteria is working
by oxidizing first ammonia and then the nitrites. The toxicity of nitrates
is not an immediate menace to your tank and can be removed from your system.



The following figure exemplifies the nitrogen "highway" in your tank;





Figure 1 Nitrogen Cycle in your tank. As you can see, nitrogen is not
recycled but has an input and an output. The preferred output is the
harvest of plants but the most common known output is by means of water
changes.



In the previous diagram (Figure 1) it is also seen that when
nitrates are absorbed by the herbivores in your tank, they don't get
extracted, they are returned to the tank in the form of excrement which
contains lots of toxic ammonia. Algae eating organisms can incorporate a
certain amount of nitrates but not enough, the surplus is sent back to your
system. Alright, they may help you keep the tank pretty but also contribute
to increasing the amounts of ammonia in your system. This may come as a
shock to many aquarists under the impression that snails and blennies were a
good way to control algae in your tank. But, as I show in figure 1, they
augment the accumulation of ammonia thus the levels of nitrites and
nitrates.



In a healthy aquarium an aquarist should ensure that the amount
of ammonia and nitrites are kept at or near zero. This will confirm that
the part of the nitrogen cycle that takes place inside your tank is working.
Now we have the difficult task of removing the unwanted nitrates. If the
levels of nitrates reach a certain level, your nitrifyers aren't able to
turn nitrites to nitrates do to saturation. This starts a chain reaction
where the nitrites reach a level of saturation that will kill your organisms
and then your nitrosifyers can't convert ammonia to nitrites. When this
happens you no longer have a system. At this moment, high levels of
nitrites will have destroyed the organisms in your tank.



What is a sustainable level of nitrates in an aquarium?



Let's make something clear, nitrates are toxic and they should
be kept as low as possible. Any conventional aquarist will recommend a
series of water changes to reduce or eliminate nitrates. Other than that,
they will refer you to buy nitrate reducing chemicals. I have a different
approach. In many scientific papers is mentioned that nitrates are toxic at
levels near 100 milligrams per liter, one paper says that at a level of
1,000 milligrams per liter it will cause the death of your fish. I
recommend a level of less than 50 milligrams per liter although my tanks had
remained near 70 for a prolonged time with no drastic effects to my fish.



The best way to remove nitrates is to know the carrying capacity
of your tank. What this means is to have the knowledge of how many fish and
other organisms your tank can support before nitrates become a nuisance.
Another great thing to know is the amount of food your fish need daily. If
you can control the intake of nitrogen (food), you've won the first battle
against nitrates. Should you want to increase the number of fish in your
tank then you have to implement my approach. By growing plants in your tank
and harvesting them regularly you are not only creating a better environment
in your tank, you are also extracting living material that contains nitrogen
absorbed from the water by these plants, NITRATES. Not only are you
removing nitrogen from your system but also phosphates and other toxic
compounds that are absorbed by these plants. I check my parameters
biweekly, in order to have a controlled system, the amount of plants removed
must match the amount of food added.



I do not encourage water changes. This measure is needed but
for other reasons and should be kept to a minimum. Adding chemicals to
minimize the levels of nitrates in your system may also contribute to
increase nitrites and ammonia not to mention the destabilizing effects on
other needed chemical reactions happening inside your tank.



To conclude this paper I will like to summarize my findings by
mentioning key aspects of a healthy sal****er aquarium;



Ø The level of ammonia should be kept at or near zero

o This means that your nitrosifyers are doing fine

Ø The level of nitrites should also be kept at or near zero

o This means that your nitrifyers are doing fine

Ø The level of nitrates should be kept to less than 50 milligrams per
liter

o This means that there is room for your nitrifyers to work

Ø Feed as less food as possible to your fish

Ø Grow as much algae and other plants in your tank

Ø When doing water changes, keep it to small amounts (10%)

Ø Don't overcrowd your tank with fish

Ø DO NOT USE CHEMICALS TO LOWER NITRATES

Ø Remember, keeping low levels of ammonia and nitrites is more
important than lowering the levels of nitrates



I hope this paper is useful to new aquarists and maybe to
advanced ones who didn't understand or were misguided on this complicated
cycle. Many local fish stores (LFS) will completely disagree with my views
but that is expected. They make lots of money by selling pre-mixed
sal****er, chemicals and other quick fix solutions to the nitrates problem.
Some even portrait nitrates as the real menace to your tank and scare
clients to a point that they invest thousands of dollars in their gadgets.
It is a win/win situation for them and a severe loss to the aquarist. If
you have to do water changes more than once every six months (some even
weekly): you can toss all your gadgets away because they are not working.



Yours truly;

???-????











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