What is cycling?
Even the most sophisticated equipment and additives available
these days can't take the place of tiny bacteria in keeping
our tanks clean and animals healthy. 'Cycling' is the process
of introducing and establishing these essential bacteria.
In a nutshell, all fish and invertebrates, including seahorses,
excrete ammonia as a waste product. However, the ammonia is
extremely toxic to them. Fortunately, there is a group of
beneficial bacteria that can convert ammonia into nitrites,
but nitrites are also toxic to our livestock. The good news
is there is a second group of microbes that can convert nitrites
into nitrates, which are not nearly as toxic. Accumulated
nitrates should ideally be kept below 10 ppm, but fish and
seahorses may show no ill-effects with slightly higher levels.
To cycle a tank, these two groups of bacteria need to be
present and established in sufficient numbers prior to adding
your seahorses or other animals. Ammonia levels will rise,
followed by a rise in nitrite levels as ammonia begins to
decline. Then, as nitrite levels begin to decline, you will
more than likely see a very slow and gradual rise in nitrates.
The appearance of nitrates is a good sign that your various
bacteria are making all the necessary conversions, however,
some tanks with a significant amount of live rock, live sand,
macroalgae, and/or are regularly maintained with water changes
may never see nitrates accumulate.
How do I do it?
There are several methods people employ to cycle a tank,
however, this article will primarily focus on two of them
— live rock and the ammonia method.
Prior to getting cycling underway, make sure your tank is
up and running and your equipment is properly functioning.
Circulation, aeration, and a stable temperature are essential
factors for the health of your livestock long-term, as well
as at the very beginning when you are establishing your bacteria
colonies. It is also a good idea to turn your tank lighting
on for several hours each day during cycling, just like you
will when the tank is stocked.
Cycling with live rock
One of the best ways to cycle a tank is through the introduction
of live rock. These are natural pieces found in the ocean
and contain a multitude of life in and on them to get your
cycling underway. Placing live rock into your new system jump
starts the cycling process. Ammonia is produced as some animals
on the rock die off and others excrete waste. In addition,
the live rock also contains the beneficial bacteria groups
needed to convert ammonia to nitrites, and nitrites to nitrates.
The time it takes to cycle a tank with live rock varies on
how 'fresh' the rock is. Rock recently harvested from the
ocean (not 'cured') will have a great deal of life on it that
will not survive the rigors of transportation and being removed
from the ocean. This rock will have a lot of die-off that
will trigger significant ammonia and nitrite spikes which
can make the cycling process last a few weeks.
There is also pre-cured live rock, which means that the vast
majority of the die-off has already occurred before you receive
it, however, further transportation can still cause smaller
ammonia and nitrite spikes. Cycling with pre-cured live rock
can still take 2–4 weeks or so.
Then, finally, there is cured live rock. Fully cured rock
that is quickly placed into your tank with minimal transportation
time, such as from your LFS (local fish store) to your home,
may 'instantly' cycle your tank. The beneficial bacteria groups
are already there in good numbers with no die-off to trigger
ammonia spikes of any significance. With fully cured live
rock you may never see the typical cycling progression of
ammonia —> nitrite —> nitrate. Your levels may initially
read — and remain at — zero, even while you are slowly stocking
To cycle your tank with live rock, an effective amount to
start with is 1 pound or more of rock per 5 gallons of tank
volume. If you plan on utilizing live rock as your chief method
of filtration, approximately 1 pound of rock per gallon of
water is ultimately recommended.
Please note that you should NEVER add uncured live rock to
a stocked, established tank. Either cure the rock in a separate
container, or make sure to purchase FULLY CURED live rock
with a very minimal transportation time from your LFS to your
After adding live rock to your tank for cycling, test for
ammonia and nitrite daily or every other day with test kits
available at your LFS. With rock not fully cured, you will
see the typical cycling progression. Then, once ammonia and
nitrites test at zero for several days in a row, the tank
is considered cycled. The time frame for this to occur can
vary widely. Factors such as the quantity and condition of
the rock, as well as overall tank health and stability (circulation,
temperature, aeration, etc.) will directly influence the time
it takes for the bacteria to sufficiently reproduce and colonize.
Testing is the only way you will know what is going on with
Cycling with the ammonia method
Another method of cycling a tank that is increasing in popularity,
is using 100% pure household ammonia. Instead of utilizing
ammonia-producing organisms to start the cycling process,
the ammonia method involves directly adding bottled ammonia
along with a starter culture of bacteria.
The ammonia must be clear, unscented, 100% pure, and with
no additives. However, you may find typical household ammonia
to be mostly water with an actual strength of only 5–10%.
Since the concentration may vary, you will need to experiment
a little to find the right amount needed to cycle your tank.
When using the ammonia method, the necessary bacteria can
be introduced to your system a couple of different ways. If
you have access to an established and healthy tank, obtain
a small amount of sand or gravel or even used filter media.
This can then be placed in the tank to be cycled and will
provide a starter culture of bacteria. Another option is to
use a commercial preparation of bacteria, such as Hagen's
Cycle, to introduce the nitrifying microbes.
After the tank has been set up and the bacteria have been
introduced, begin to add the ammonia. If the tank is on the
smaller side, start with only a couple of drops. Let it circulate
in the water for a short time, and then test for ammonia.
You want to raise the ammonia level to about 1–2 PPM
Continue adding drops of ammonia and testing, while keeping
track of how many drops total it takes to get to 1–2
Once you've reached the desired level, you now need to wait
for the bacteria to multiply and do their job. It may take
several days to a couple of weeks for your ammonia test to
register zero. Once it does, add the same number of drops
of ammonia again. Keep repeating this many times, each time
waiting until ammonia reads zero, until finally the ammonia
test goes to zero within 8–12 hours of the addition
When the tank is able to clear the ammonia within this time
frame, that means that there are large numbers of bacteria
present. At this time, test for nitrites. If nitrites are
present, perform 3v4 more ammonia cycles to further establish
the second group of bacteria. If the nitrite test reads zero,
perform a very large water change and then you can begin slowly
stocking your tank.
It's been suggested that elevating the temperature of the
tank to the mid-80s F during cycling with the ammonia method
can have beneficial effects. Just make sure that there are
no animals in the tank being subjected to this temperature
extreme (and ammonia), and also make sure to lower the temperature
again prior to stocking.
Also, tanks with low alkalinity may experience pH spikes
with the addition of household ammonia. These spikes may also
hinder the growth of the necessary bacteria. To counteract
the problem, use a good buffering product prior to cycling
with ammonia, and perform a large water change after cycling
(prior to stocking) to get pH levels back on track.
What about cycling a tank with fish or other animals?
Several decades ago, when people were first setting up marine
tanks, the conventional method of cycling was to use a hardy
fish or other animal to introduce ammonia into a new system.
However, by using live animals you may be introducing a parasite
or pest to your new tank. In addition, the animals are being
subjected to toxic ammonia and nitrite levels, which is unnecessarily
cruel. When there are other safer and gentler ways to cycle
a tank, there is no need to use live animals.
When can I start stocking?
Once your ammonia and nitrite levels are at zero, whether
it be from cycling with live rock or several cycles with the
ammonia method, you are close to being able to stock your
If you used a skimmer during cycling with live rock and/or
did not have extreme ammonia or nitrite spikes, you will probably
only need to perform a standard 10% water change prior to
stocking. If you did not use a skimmer and/or you registered
significant ammonia and nitrite levels with a lengthy curing/cycling
process, you will need to perform a more significant water
change, such as 50–75%.
As mentioned earlier, since the ammonia method may cause
problems with pH, a very large water change, approximately
90%, will be necessary following the use of this method, prior
to the introduction of animals.
When ammonia and nitrites test at zero, nitrates are <10
PPM, pH is between 8.0–8.4, water changes have been
performed, and equipment is functioning properly, you are
ready to start stocking your tank.
Try to keep nitrates at 10 PPM or less. If nitrates are high
or continue to climb over time, more frequent water changes
and/or the addition of macroalgae will help bring them down.
If your pH is below 8.0, add a high quality buffer to raise
your alkalinity and pH.
How do I stock?
Patience is a virtue with marine tanks, and stocking too
many animals too soon can have disastrous effects. Start with
a very small number of animals (acclimated properly), and
test the water daily for several days after introduction for
any ammonia or nitrites. If ammonia and nitrite levels consistently
read zero, continue to to wait for at least two weeks before
adding any new animals to allow time for the bacteria to multiply
and effectively handle the new load.
If you ever find your ammonia and/or nitrite levels approaching
.4 PPM or greater in a stocked tank, you will need to act
fast. Diluting the toxins in the form of one or more large
water changes, adding more bacteria (live rock, 'seeded' media,
commercial products, etc.), the addition of macroalgae or
a chemical filter to absorb the toxins, or temporarily relocating
the animals to another tank are all effective ways to handle
an ammonia or nitrite spike.
Do I need to test after cycling is complete?
Even after cycling is long over, it's a good practice to
periodically test for the presence of ammonia, nitrite and
nitrate, especially after adding new livestock. Equally important
is knowing your tank's pH range, and making sure that it stays
between 8.0–8.4. (Your pH will typically be lower in
the morning before your lights come on, and higher in the
evening just after the lights go off. )
Catching a potentially serious problem early and taking immediate
steps to correct it can help prevent a lot of heartache.