Fishless cycling is an easy method of getting
your new aquarium ready for the safe introduction of fish. It
does this by preparing your filtration system to handle the toxins
that your fish will excrete once introduced. An unprepared filter
system would allow those toxins to build to harmful or even lethal
When fishless cycling, you will be adding an ammonia source to
an aquarium to simulate the ammonia additions that would normally
come from the fish. Bacteria that you will sometimes see referred
to as 'nitrifying bacteria' will use this ammonia for fuel and
they will build in numbers to colonize your filtration system.
These beneficial bacteria will convert both toxic ammonia and
nitrite to much less harmful nitrate.
I wrote this article with the intention of giving you just enough
information to fishless cycle successfully without overwhelming
you with many scientific details. You can find plenty of information
on the science behind fishless cycling in articles elsewhere.
I refer to some of this information later. I have also included
common questions and problem situations regarding fishless cycling
that I have encountered over the years.
Advantages of fishless cycling over cycling
with fish -or- Why should I bother with this?
The biggest advantage to fishless cycling is that you can safely
stock the aquarium without subjecting your new fish to toxic levels
of ammonia or nitrite. Elevated ammonia and nitrite levels are
capable of doing long-term damage to fish. Even if the fish survive
and seem to not be affected, some harm may have occurred. You
may not see the effects right away, but the damage done to a fish
can affect the long-term health of the fish and shorten its life.1
Chronic exposure to low ammonia levels can cause gill and kidney
damage among other maladies.2 Fish differ
in susceptibility to these toxins. Short-term exposure can affect
some fish more than others. Any time you cycle with fish and subject
them to elevated levels of ammonia or nitrite, you put the fish's
long-term health at risk.3
Another advantage of fishless cycling is that you can add all
of your fish at one time. This can be very beneficial when stocking
with aggressive cichlids. Introducing potentially aggressive fish
together allows all of them to stake out and claim a territory
without having to challenge those that are already well established.
The new fish will have been stressed already from transport and
introduction to a new aquarium. Long term, unalleviated stress
has been shown to negatively affect the health of certain fishes
during transport. If the fish has to also deal with the harassment
of established aquarium occupants, the physiological changes that
occur during stress will continue and can threaten the fish's
health and survival.4 Adding your fish all
at once can also be beneficial if you're ordering from an online
supplier, as you'll save on shipping costs and not have to deal
with multiple shipments.
Myths about fishless cycling
Myth #1 -- Fishless cycling takes longer than cycling with fish.
In some cases, this could seem to be true. If you cycle with a
few small fish that are excreting a minimal amount of ammonia,
you will need to only build a small bacteria colony to handle
that ammonia. This takes less time than building a bacteria colony
that can handle a full load of fish. However, you would then proceed
to slowly add additional fish and wait for the bacteria colony
to increase enough to handle the additional load. You need to
continue repeating this process of adding a few fish until the
full stocking of the aquarium is complete. So, you may cycle more
quickly initially, but the bacteria are only able to handle the
initial small load of fish. To get the aquarium up to full load
and capacity will take a few weeks, even when cycling with fish.
Myth #2 -- Fishless cycling is complicated.
I will hopefully dispel that myth below. Some methods I have seen
are a bit complicated, very true, but unnecessarily and to no
advantage, in my opinion.
Here is a quick summary of steps.
Work out your formula for your initial ammonia dose and
add that to the aquarium.
Test for ammonia every 24 hours until you get a reading
Add ammonia every other day while testing for nitrite.
Do small partial water changes.
When the nitrite test reads zero, do a series of small,
partial water changes to bring nitrate down.
Add the last dose of ammonia 48 hours before adding fish.
It is no more complicated than that.
Detailed steps to fishless cycle
--Get your aquarium set up, filled with water, filter(s) running,
and water up to a temperature of about 85 degrees, as warmer temperatures
can accelerate the growth and multiplication rate of nitrifying
bacteria.5 Keep your aquarium lights off
for now, as there's no reason to run up the electricity bill and
encourage algae to get off to a good start before you even have
fish in the aquarium. If you do decide to run the lights, don't
worry about any haziness in the water during the cycling period.
If you are intending to use power heads or other water movement
pumps to circulate the aquarium water, get them in place and running
because nitrifying bacteria may be inhibited by low oxygen levels
in the water.5 Nitrifying bacteria need
oxygen just like fish or other aquatic creatures. The circulation
of the water will help to keep oxygen levels high.
--Test your water's pH and KH. It is best for cycling if pH is
7 or above and KH is at least 4 or 5. If your pH is low, (below
6) then the bacteria that are responsible for cycling an aquarium
may be inhibited.5 If pH is fine, but KH
is low, then the stability of your pH may be in jeopardy. A moderate
KH level is needed to stabilize pH. Therefore, a pH of 7 today
might be 6 or less tomorrow if KH is only 1-2. If your pH and
KH levels are fine, then don't worry about making them ideal for
your fish for now, just move on to the next step. You can fine
tune water parameters later, if needed. (For more info on how
to increase pH and KH, there are excellent articles in the forum
library under the 'Chemistry'
section titled 'Practical
Water Chemistry' and 'Rift
Lake Buffer Recipe'.)
--Add ammonia at the rate of 2 drops per gallon. Why add 2 drops
per gallon? It is just a starting point, that's all. You can start
with less if you like. Wait 20 minutes for the ammonia to circulate
and fully mix into your aquarium water and then run the ammonia
test. (If you are not sure what kind of ammonia to add, see 'What
kind of ammonia should I use and where do I get it?' under
'Frequently Asked Questions' below.) You are aiming for
an ammonia level that is somewhere between 1-2ppm. (See 'What
does ppm mean?' below.) By the way, there are about 100 drops
in a teaspoon. It may be easier to measure out your ammonia dose
with a teaspoon rather than an eyedropper. In addition, keep in
mind that hobbyist test kits are not precise and that is ok because
you do not need a precise reading. If the ammonia level looks
somewhat like it is in the proper range, then that is good enough.
Those color cards that come in the test kits can be very tough
If your ammonia level is low, then calculate how many more drops
you need to add in order to raise it up into the desired range.
For instance, if your ammonia level is now .5ppm, then add another
2 more drops per gallon. So for say a 20 gallon aquarium, add
another 40 drops. Test again after 20 minutes to confirm that
it is now in a good range. If it is still low, then add more while
keeping track of the total amount of ammonia (drops, teaspoons)
If your ammonia level is too high, say 3-4ppm, that's ok. Just
make a note that future doses only require half of your initial
dose. So, your formula might be 2 drops for every two gallons
instead of every gallon. You could always do a water change to
bring the level down to 1-2ppm, but this is only necessary if
you have overdosed to a level above 5ppm. A very high ammonia
level will inhibit the nitrifying bacteria responsible for cycling.5
Be sure to make a note of the total drops/teaspoons added. You
will need this information later.
--At about the same time each day test your aquarium water's ammonia
level. Do not add more ammonia just yet. That comes in
the next step. It will seem like the ammonia level is never going
to drop, but it will, so be patient. It can take anywhere from
7-10 days, typically. You will not necessarily see a gradual decline,
but more of a sudden drop. You may get a slight reading of .5
or so one day, and then get a zero reading the next. When you
get a reading of zero, you are ready for the next step. Do not
start adding more ammonia on the day that it starts to decline.
It is not necessary. Wait for the test to indicate that it's zero.
(I would suggest that if you are not familiar with the nitrogen
cycle that you read the excellent article in the forum library
under the 'Chemistry'
section titled 'The
Nitrogen Cycle'. It is not necessary to understand the details
of the nitrogen cycle in order to fishless cycle, but you may
find it helpful to understand something of the processes involved
if questions or problems arise. So, while you are waiting for
that ammonia to drop, take some time to check it out.)
--Now that ammonia reads zero after 24 hours, you will need the
note that you made regarding your initial ammonia dose. However
many drops/teaspoons you added initially, add that many again
now. You will add this same dose every 2-3 days. Go for consistency,
but it is ok if you forget or get busy and skip a day. It will
not derail the processes that are happening. In addition, you
do not have to add the dose at exactly the same time each day,
but best to be somewhat consistent when adding and testing. Try
to set aside a time each day for this.
--Now that you have built up enough bacteria to convert ammonia
within 24 hours, you can stop testing for ammonia and begin testing
for nitrite. The nitrite drop can take up to 2-3 times as long
as the ammonia drop. This length of this phase can lead some to
think that the cycle is not progressing. However, it is progressing,
so be patient. You will probably get a nitrite reading that is
very high, even off the chart. That is normal. In order to ensure
that things speed along just as quickly as possible, you can perform
partial water changes to keep the byproducts of nitrification
down because just like excessive ammonia levels they will inhibit
the nitrifying bacteria.5 You can perform
these water changes daily. However, I would suggest not changing
too much water at one time. Try 30% or so daily. (See why in 'Cautions,
tips and tricks' below.)
Here is what your daily routine going forward will look like:
Test for nitrite, perform water change, and then add ammonia.
Next day; test for nitrite, perform water change.
Next day; test for nitrite, perform water change, and then
Next day; test for nitrite, perform water change.
Next day; test for nitrite, perform water change, and then
The daily tests of nitrite will let you know the effect of the
water changes on the nitrite level. You are looking for a zero
reading, of course, but that can take a while. Only test for nitrite
once per day, about the same time each day. Again, do not test
any longer for ammonia. We can assume it will be zero each day
now. Make an effort to keep nitrite down below 5ppm by way of
small, partial water changes. The ammonia additions will ultimately
raise the nitrite level while the water changes will drop it back
down. Do not over analyze the test results. You are just looking
to see if the water changes that you are performing are adequately
keeping nitrite down. You are ultimately looking for a nitrite
reading of zero.
--The next and final steps begin when you do finally get that
nitrite reading of zero. Like ammonia, you will not see a gradual
decline in the nitrite level, but instead you will see more of
a sudden drop over a day or two.
--Now that nitrite is also being converted within 24 hours, it
is time to start testing for nitrate. Notice that we have not
done the nitrate test yet. Do not get tempted to test for nitrate
sooner than this. Check out the section titled 'Testing for nitrate
with nitrite present' under 'Cautions, tips, and tricks' below
for more of an explanation.
--Perform a series of partial water changes over the next day
or so in order to get nitrate down to 20ppm or so. Avoid the temptation
to do one massive water change. Treat your new colony of bacteria
like a delicate, fragile living thing. I have seen massive water
changes on a newly cycled aquarium result in a temporary nitrite
spike. It does not always happen, but why risk it? The last thing
you want to see after finally getting a zero readings are small
spikes. If they do happen, I have found that these spikes are
small and brief, so no major harm done.
--Continue adding your ammonia dose every other day or so until
you add your fish. Add the last dose of ammonia 48-72 hours before
adding fish. This will give you time to do any final water changes
to get nitrate levels down without fighting the addition of new
nitrate resulting from the addition of more ammonia. This will
also provide time to ensure that the filtration has fully converted
all of the ammonia and nitrite into nitrate before adding fish.
--The last step is to add your fish.
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