Cycling Without Fish
Written by Chris Cow
Ph. D. Organic Chemistry
For many years, the common method of cycling a tank has been to set everything up, then
add a few hardy or "disposable" (a term that I personally find somewhat
offensive) fish, then wait 4-6 weeks until the bacterial colonies which convert ammonia
into nitrites into nitrates have become established. It is very common at this point for
the stress caused by toxic ammonia and / or nitrites to kill some or in extreme cases all
of your starter fish, no matter how hardy they're supposed to be. In addition, it's a well
known fact that the damage caused by high ammonia levels to the gills of a fish is, to
some extent at least, permanent. Once the tank has been fully cycled, you can start adding
fish slowly, usually at a rate of a couple every week or two, until capacity is reached.
This slow addition allows time for the relatively small bacteria culture on your filter to
grow until it can handle the increased bioload. If done incorrectly, for example by adding
too many fish at once after the cycle, an ammonia/nitrites spike can occur before the
bacterial colony can adjust.
What is the effect of the fish added during cycling? Quite simply, through their
digestive tracts and the food that we feed them, they are a source of ammonia, which the
beneficial bacteria require to live and to multiply. While the above method is the
traditional way of cycling a tank, it is neither the only nor the best way.
In order to properly cycle a tank, all that's required is the filter media, water
movement (to supply oxygen to the bacterial colonies, an introduction of the right type of
bacteria, and a source of ammonia. The best and most efficient source of ammonia is
(surprisingly) pure ammonia. The household cleaning variety is perfect for this use, but
make sure that it does not contain any additives or perfumes before using!
In order to cycle a tank using ammonia, start everything up and add some gravel from an
established tank or a few potted plants (their roots contain all of the necessary
bacteria, and the plants themselves do not seem to be harmed by this process). Then simply
add 4-5 drops of ammonia per 10 gallons per day until you get a nitrite spike. Once you
have nitrites, cut the ammonia back to 2-3 drops per 10 gallons per day until the nitrites
disappear. When you get a 0 ppm nitrites reading, you have a fully cycled tank.
The advantages to this method are several. First and most importantly, in my reckoning,
is that no fish are harmed during the cycling process. This means that you don't have to
risk the fish you really want in the tank to a nasty death, or alternatively, find a new
home for several fish that you were using to cycle the tank and no longer want. Secondly,
no matter how cheap the fish, I can guarantee that 10 or 20 mL of ammonia is cheaper!
Thirdly, and this is of particular interest, the tank will cycle much faster by this
method. I have used this method twice, the first time was on a 45 G tank with a fluidized
bed filter, the second was on a 10 G tank with a lowly sponge filter. The time for
complete cycling of these tanks was 12 days and 14 days respectively. Compare that with
the standard method which averages 4-6 weeks.
Finally, once the tank has been cycled, the bacterial colony created by this method can
handle a large bioload immediately. The amount of ammonia added to the tank during the
cycle is significantly higher than what would be contributed by a small number of hardy
fish, therefore, a much larger, healthier bacterial colony exists at the end of the cycle
using ammonia than would if you used fish. After cycling my 45 G, I immediately added 6
bosemani rainbowfish, 3 clown loaches and a plecostamus. This is far above the recommended
stocking levels at the same stage if I had cycled with fish. All of the fish are very
healthy, and there was no ammonia or nitrites spike after the addition of the fish.
The benefits of this method are obvious, and as far as I can tell, there are no
disadvantages. Overdosing isn't a problem since there are no fish in the tank. Stop
needlessly stressing / killing your fish. The next time you have a tank that you need to
cycle, try this out. I guarantee you'll be pleased with the results.