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It may
well be the very first thing you - a new fish hobbyist - should read about. It
is also the single most important factor that can go wrong and result in heavy
fish losses. Therefore it usually is the reason for the disappointment that
makes people leave this beautiful and rewarding hobby. Yet, things are very
simple and the problem can be avoided if simple steps are followed. Cycling the
tanks actually means establishing the correct elements that will take care of
the Nitrogen cycle. If this is not achieved at the beginning then, when fish is
added in the tank, the “new tank syndrome” is observed with – usually –
fatal results. Well, too many terms already and the least I would like is to
confuse you.
Cycling
the Tank and the Nitrogen Cycle. Life mainly consists of four elements: Carbon (C), Oxygen (O), Hydrogen
(H) and Nitrogen (N). Other elements are usually present but these four elements
are always there since they are the elements that form the proteins, the
“bricks” every living organism is made of and the nucleic acids which are
the “core” of life. So fish, like all living creatures take these elements
with their food, use them and then excrete all that is not needed. Usually fish
excrete these four elements in the form of carbon dioxide (CO2), urea
and ammonia (NH3). It may seem strange but we, humans, do exactly the
same. Urea is subsequently “broken” in carbon dioxide and ammonia too, so we
have two new entities in our water. Carbon dioxide, being a gas, will eventually
leave the water (filters and aeration will shorten the time needed for this)
leaving only the ammonia issue. Unfortunately ammonia (NH3) will not leave the
water and is very toxic to the fish even in small quantities. Actually, ammonia
reacts with water to form ammonium hydroxide (NH4OH). One way to deal
with this is to change the water every day or even more frequently (if the fish
load is high) but this is not practical. Fish keeping is a hobby not a way to
develop an impressive muscular system. Another way is to use something that will
absorb it. There are some materials that do exactly that but usually these need
to be replaced very quickly, may not work in some special environments (in tanks
where NaCl is added either for treatment or to increase salinity) and are not
the natural way to do that. Yes, there is a cheap (in fact free of charge) way
to do that. There are two bacteria that live in the water, so they are already
in your tank when you fill it with water. The names (for those interested) are Nitrosomonas
and Nitrobacter and are called “nitrifying”, “useful”
or “beneficial” bacteria. These are aerobic bacteria, which
means they need oxygen in order to live, thus they are usually found in places
where there is high water flow (mainly in the filters). There, they will form
colonies and start the work. Their work is to take the oxygen, bind it to the
ammonia and transform it to nitrites (NO2-) and then to
nitrates (NO3-). What happens in detail is the following
set of chemical reactions:
Nitrosomonas
: 2 NH3 + 3 O2 è 2 HNO2 + 2 H2O + Energy
The
amount of energy released in this reaction is used by the bacteria for their own
biochemical reactions. The nitrous acid formed in this reaction is a weak acid
and decomposes in the water giving hydrogen ions (H+) and nitrite radicals
(NO2-). Nitrous acid (or nitrites) will not stay for long in the
water because the second type of bacteria will use it as a source of energy
according to the following reaction
Nitrobacter
: 2
HNO2 + O2 è 2 HNO3 + Energy
Again,
the bacteria for their own biochemical reactions use the amount of energy
released in this reaction. The nitric acid formed this way is a strong acid,
which will decompose in hydrogen ions (H+) and nitrate radicals (NO3-).
Nitrates can be used by all plants (including algae) for their own biochemical
reactions and will be readily removed from the water in a planted aquarium.
Please note the necessity for oxygen in both reactions.
Each of
the two species is dedicated to perform only one type of reaction. It should be
noted that nitrites are less toxic than ammonia (but still very toxic) while
nitrates are far less toxic. This is called biological filtration. The
bacteria can’t further transform nitrates, which can either be removed by
water changes or consumed by plants if your tank has enough of them. Why don’t
the bacteria “eat” the toxic ammonia at once? Simply, because there are not
enough of them in your tank. What you need to do is give them time and ammonia
in order to multiply and be able to sustain more fish load. This is called
“cycling the tank” or establishing the Nitrogen cycle. Typically, the
ammonia will go up initially and then nitrites will start to increase while the
ammonia levels drop. Finally, nitrites will also fall and nitrates will
increase.
New Tank Syndrome is the situation
where the ammonia is getting higher and higher while the useful (or beneficial)
bacteria are growing in numbers. If the fish load is too high from the
beginning, the bacteria can’t grow fast enough so the ammonia levels get
higher and higher, soon reaching toxic levels. The result is death to the fish.
Fish
Cycling. In order
to avoid this, the fish keeper should add only one or two small fish in the tank
and wait until the ammonia levels rise and drop. Bearing in mind that something
may go wrong, these fishes should be cheap and hardy, not the ones you want to
keep in the end. Since the ammonia production will be low (keep feeding at a
minimum) the bacteria will have the time to grow and reach the right numbers for
this fish load. When the ammonia levels have dropped he can add some more fish,
take ammonia measurements and repeat this procedure until the whole fish
population is in the tank. The bacteria colony established this way will sustain
this fish load as long as nothing happens to it – something we will discuss
later on. This is the natural way to do it and has the advantage that the
bacteria in the tank are proportional to the fish in the tank and the feeding
habits of the fish keeper. The disadvantage of this method is that you may lose
a fish or two during the process or you may end up with some fish you don’t
really like but were the cheaper you could find. I must emphasize the fact that
after setting up many tanks I have never lost a single fish during cycling. What
you need is the basic knowledge on what is going on and patience – never force
things to happen.
Fishless Cycling. This is another way
to cycle the tank. The idea behind this is to provide the bacteria with their
food without actually adding any fish. In short, the fish keeper will daily add
a small quantity of ammonia while normal filtration is working. The bacteria
will soon grow and the tank will be cycled. I have heard many recipes which vary
greatly and as long as you are going to perform an almost complete water change
before adding any fish you can add as much ammonia as you want (within reason of
course, a distinct ammonia smell is a direct proof that you have gone too far).
The advantages are no fish losses, no unwanted fish and perhaps a shorted
cycling time. The disadvantage of this method is that you can never know if the
bacteria colony is enough to sustain the whole load of fish you had in mind.
Adding fish gradually is one way to bypass this but then the biggest advantage
of this method is lost. On the other hand, if the colony is too large for the
amount of ammonia your fish actually produce, some bacteria will starve to death
and pollute your water.
Adding
a Bacteria Culture.
Some people prefer to “boost” the cycling process a bit in order to reduce
the time it takes and to make sure they are on the safe side. There are many
products commercially available, which contain live bacteria and can be added in
your tank during the cycling process. In my experience I have never seen any
additional benefit from this addition but they worked well when an established
tank got off balance.
Seeding
the Tank. This is
perhaps the best way to go but it has one small drawback. It assumes you already
have an established tank in place (or a friend of yours has one). You may seed
your tank with bacteria from the matured tank. Bacteria are located everywhere
but are usually found on porous surfaces, especially in the filter material. You
can take some of the filter material from the old tank friend and put it in your
filter. You may also take some water, gravel or rocks from the matured tank.
Another way is to add the filters you intend to use in your new tank in the
matured tank and let them run for 10 days. I usually have at least 2-3 sponge
filters running in my tanks, just in case I need to operate one more tank (for
raising the fry or isolating a fish). If the new tank is considerably bigger
than the old one I always use a nylon stocking to put the ceramics (or any other
porous material meant for bacteria colonization) in an then place this in front
of the outlet of the filter. After 10 days, the ceramics will be full of
bacteria. You may then take them out and transfer them in the filter of your new
tank. If you can combine this with some “old” water you should encounter no
problems. I feel the last method is the best only because you will use the same
bacteria that have been used to your water conditions. That aside, it is the
safest and fastest method to cycle a tank. I have repeatedly used this method
and I usually add the full fish load within one week (even in my 1300 liter
non-mbuna tank) after the addition of water. Following this method, I have never
experienced any ammonia spikes, neither any fish losses (not during this stage
anyway). Technically speaking, I used all the water of my matured 100 liter tank
when I was cycling my 500 liter tank and then I used 300 liters from this tank
(a year later of course) to cycle the 1300 liter tank.
Starting
Cycling with Plants.
Well, no secrets here. This combination is the best of them all. You may just
cycle the tank with fish or without them but you have some healthy (preferably
fast growing) plants in the tank. This will complete the nitrogen cycle and will
not result in a tank full of nitrates. I have tried this process when setting up
my 500 (125 gallons) and 1300 liter (340 gallons) tanks, combined with the
described “seeding” technique. In both cases, the full load of fish was
added within one week and I have never experienced an ammonia or nitrite /
nitrate spike. Needless to say, although I am quite confident that I am doing it
right, I take two measurements for ammonia, nitrites and nitrates per day for
the first week, one measurement per day during the second week and one
measurement per week for the rest of the first month.
Now you
have your colony bacteria in place but you should always keep in mind that this
colony is alive and, although it will not require any special care from you,
still there are some things, which you should always keep in mind.
Unfortunately, this bacteria colony can be destroyed under certain circumstances
and the fish hobbyist should know that. If he doesn’t pay any attention he may
have to cycle the tank again. Cycling the tank with a full fish load is very
risky, painstaking and sometimes everything can (and will) go wrong.
What can destroy your
colony of useful bacteria?
Filter
malfunction or power shortage is a very common situation which usually results in severe damage of
your bacterial colony. As said at the beginning these bacteria are aerobic, they
need oxygen to live and it is this oxygen they use to transform ammonia to
nitrites / nitrates. When the filters are not working the oxygen content of the
water drops dramatically and – if this goes on for a while – it will soon
drop below the level that can sustain these bacteria. This, depending on the
initial oxygen content of the water may happen within 2 – 24 hours. Apart from
losing the beneficial bacteria and their biological filtration capacity, your
tank water will soon be filled with debris and organic pollutants. It is very
important to perform a water change every time your filtration system stops
functioning for more than 3-4 hours.
Medication
is another reason to lose your colony of useful bacteria. Some medications while
killing the unwanted pathogens will also kill the useful bacteria. Usually the
medications work by attacking basic structures or biological pathways of the
microorganism so the beneficial bacteria will be “attacked” too. It is
always a good practice to examine the small letters of the product you are about
to use to make sure that your bacteria will survive. If you can choose, you
should always opt for the medication that will not harm them. Some of the
medications that will harm your bacterial colony are listed here for easy
reference. Chlortetracycline (10 mg / litre) and oxytetracycline (50 mg / litre)
are known to affect the beneficial bacteria. Formalin (15-25 mg / litre) has
been shown to have variable effects on the nitrogen cycle. Methylene blue (1-8
mg / litre) can cause a severe and prolonged interruption to nitrogen cycle.
When using one of these medications, the fish keeper should prefer the use of an
isolation tank and treat the infected fish there. He should be very cautious and
change the water every other day assuming that, despite any filtration there is
no biological filtration in the tank. I recommend an 80% water change every
other day and addition of new medication for compensation. Other medications
will leave the nitrogen cycle unharmed and should be preferred whenever
possible. Thus, copper (up to 0.5 mg / litre), nifurpririnol (up to 1 mg / litre)
and sulphamerazine (up to 50 mg / litre) will leave the nitrifying bacteria
unharmed. It should be noted that these observations have been made for
freshwater aquaria. The same medication may exert a different action in
saltwater tanks.
Changing
Filter Media. As
already said, filter material is the place where huge colonies of bacteria
reside. The filter floss, the ceramics, any porous material you have added, is
the house of millions of bacteria. Sometime your filter will become clogged
because of the detritus or other particles (food, sand etc.). This is readily
recognized by the reduced water flow from the filter’s outlet (visible at
once, if the outlet is directed to the surface – a very useful practice) and
it is time to do something about it. You unplug your filters and remove all the
clogged material replacing it with new one. This will guarantee you that the
filter will regain the original water flow but it is a mistake. What you did is
to throw away billions of bacteria and now your tank is in danger. The remaining
bacteria (on the gravel, the glass, plants everywhere) are only a small portion
of the bacteria that worked for nitrification. However, the fish load is again
the same. Under these circumstances, the bacteria will have to grow in numbers
until they can cope with the fish load. More often than not, this will result in
a “new tank syndrome”. What’s worse, since this is not a new tank but a
tank with a normal fish load, it will take longer and the results will be
evident very fast. Therefore, when you have to change the filter media do not
change all of it. Always leave part of it behind. If you have two filters
running in the same tank (I usually have up to 6) then you can clean thoroughly
half of them, add new material and then wait for 2-3 weeks before cleaning the
others. If you have only one filter, you can use water from your aquarium to
gently clean the floss or sponge and then put it back in the filter. You should
not use tap water because chlorine will kill your bacterial. Only use aquarium
water or lukewarm fresh water in which a chlorine / chloramines remover has been
added. For safety reasons, use double the recommended quantity.
Measuring
Ammonia, Nitrites and Nitrates. It is clear that taking measurements for the nitrogen compounds in your
tanks is of paramount importance. It is an easy task, won’t take more than 3
minutes and may save your fish. Indeed, an elevated ammonia reading is a warning
sign but there are quite a few things you can do. The most important thing is
the one you must not do – panic. The first thing is to make a
large water change (provided your fish will take it – Tanganyikan cichlids are
a clear exception to that), add new bacteria from a commercial preparation and
– if available – add a seeded filter from a matured tank. It is always a
good practice to refill this tank with some water from an old aquarium (plus
fresh water of course). Please note that ammonia is far more toxic in alkaline
pH whereas it exists in the form of the far less toxic ammonium (NH4+)
in acidic pH. Consequently, aquaria housing cichlids from the African Rift Lakes
(with a recommended pH between 7.5 and 9) should be monitored far more
frequently. Elevated nitrite levels mean that for some reason, the nitrogen
cycle is malfunctioning and the second step of nitrification is not working.
Again, a water change is a must. If possible, you can raise your pH above 7
(alkaline) to avoid the formation of nitrous acid until the second step of
nitrification is established again. You should keep in mind that this should
only be done gradually in cases where the initial pH was a bit less than 7.
Elevated nitrate levels is an indication of heavy feeding, decaying organic
matter (uneaten food, dead fish or plant) or improper maintenance of the tank as
far as water changes are concerned. A massive water change is a must and will
sort the problem immediately. Whenever a massive water change is recommended, I
prefer to make 2-4 small water changes at 45-minute intervals, to reduce the
stress of the fish. Nitrates, nitrites and ammonia are toxic substances but even
their removal must be done with care. Removing 95% of the water instantly and
replacing it with fresh water forces the fish to adapt to a new environment at
once. Planted tanks are less prone to elevated levels of nitrates since plants
will use them as food.
There
are many ways to take measurements for these pollutants. One way is the
“visual” method which is useful only when there is too much pollutant in the
tank. Thus, the water may take a “yellowish” tint which should warn you. The
disadvantage is that you can only “see” this tint when the concentration of
the pollutant is already too high. In many cases, dead fish may warn you
earlier.
You can
use the special kits available in the market to measure for Ammonia / Ammonium,
Nitrites and Nitrates. Usually all it takes is to get some water from your tank,
add some drops from the kit, wait for some minutes and then compare the final
color of the solution to a given color table. Although far from analytical
accuracy, still they work and, believe it or not, they are accurate enough.
Sticks
work by dipping them in the tank water and then wait for a specified amount of
time until color forms (usually on special pads). You then compare the color to
that of a given color table. Sticks are less accurate but are handy, easier to
use and faster. Although more expensive (on a per test basis) they usually test
for 4-6 analytes so they will give you an overall estimation of your tank water
in an instant.
Sometimes,
you may find out that a tank has gone off balance and needs a quick action. The
usual recommendation your petshop will give is to add an “ammonia absorbing”
agent. Well, if you keep discus
this will probably work. If you keep African Rift lake cichlids it probably
won’t. What the petshop will usually forget to tell you is that if salt is
present in the tank, this absorber is useless. In fact, common salt is used to
regenerate the absorber. What’s
worse, the absorber will not solve your problem, it will only treat the symptom.
I always prefer to follow the steps I described earlier because this is the only
way to find what the causing agent is and how to fix it permanently.
I believe that the
wonderful hobby of fish keeping is a rewarding one. I also believe that the
successful keeper is one who has blended the important ingredients in a perfect
blend : art and science. While this article may not
answer all your questions or solve all your problems it will help you to
understand what lies behind this “cycling” thing – which will make you a
better hobbyist.
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