Cycling a Goldfish Tank

What Every Fish Keeper Needs to Know about Cycling their Aquarium

One of the most critical elements every goldfish owner must understand is how to cycle their tank.  This is necessary in order to provide a stable environment for their aquatic community and prevent health issues that result from New Tank Syndrome, a serious and often fatal condition caused by unbalanced water parameters.  Achieving stability in a tank’s ecosystem can only be done through the nitrogen cycle, the process which is covered in detail in other articles.

In this post, we are going to cover how to cycle your goldfish aquarium so your goldfish can thrive.

What You will Need for Cycling

You will need to have an appropriately sized tank that has set up with substrate, a filter, and some decorations for the fish to hide in once they arrive. The tank should also be filled up to the brim with water that has been treated by a conditioner that removes chlorine.

You will also need an ammonia source to kick-start the cycling process. This can come from fish waste (produced by fish), degrading material such as food or plants, or straight from a bottle (as sold in hardware stores for cleaning, called Ammonium Chloride).

You will also need a water testing kit so you can keep track of your progress in the cycle and know when it is safe to add fish.  The last thing you will need is a source of beneficial bacteria to start your colony.

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Starting the Cycle

Once you have everything ready, you must get that filter running. The cycle cannot complete unless a filter is continually at work.  When it comes to introducing an ammonia source, some people will purchase cheap “feeder fish” (which are really small common and comet goldfish) sold by the thousands in pet stores to get that ammonia going.  However, some have raised objections over subjecting them to the very dangerous conditions of an uncycled tank and prefer to use the liquid version. (It may also be worthy to note that feeder fish may introduce harmful pathogens into the tank and cause the goldfish you want to keep for pets to come down with disease.)

If you choose to use live fish, the ammonia will start to accumulate from the time you place them in the tank.  If you choose to use the liquid chemical, you will need to put it into some kind of a container that dispenses by drops.  Also, be sure you keep this well labeled and out of the reach of children!  It may also be helpful to note that the latter method enables you to crank up the temperature (86 degrees Fahrenheit to 95 degrees Fahrenheit) which will speed up the process, but without frying any fish.

The Cycling Period

Keep the tank well oxygenated to promote the accumulation of good bacteria. This can be done by ensuring that the flow of the filter has a some distance to fall before touching the surface of the water, making more water agitation.  An airstone can also help with this.

Before adding the ammonia source, you will need to “condition” the tank with beneficial bacteria which can be derived from the filter media of a previously established tank or from the pet store in a bottle (I use Top Fin’s Beneficial Bacteria, but a similar brand will do fine).  After waiting at least an hour, you may add one drop of ammonia for every gallon EACH DAY or introduce your ammonia-producing fish (in which case you will not need to add ammonia by hand).  Yay, you say, I will have to do less work if I use live fish.  Sorry – daily water changes of at least 20% are required to prevent your fish from dying and stopping the cycle abruptly before it finishes, so that actually might prove to be more work.

After a few days, if you are using the liquid chemical version, test the water successively every day for ammonia.  You will probably see a large spike of it on your first test.  This is normal.  Continue to test daily and look for nitrites.  They might take some time to appear, but don’t forsake the adding of the ammonia!  After you get a reading of nitrITES, watch your successive readings for nitrATES.  The ammonia level will begin to decrease until it reaches 0ppm.

You will want to continue adding ammonia even after it reaches 0ppm until the day before you get your new fish.  When this happens – and it might take up to 8 weeks – you will  be able to add your new goldfish friends.  Adding them before the ammonia level goes back to 0 can jeopardize their lives, so please make sure your tank is safe before adding pet goldfish.  It is recommended to do a large water change (50 to 90%) the day before getting them, and do not add a large batch of new fish all at once or you risk spiking up the ammonia again… one at a time is best!  After that, you may do weekly water changes and add beneficial bacteria on occasion to counteract an ammonia spike from, say, overfeeding.

Now you know how to cycle your goldfish tank!  Hope this has been helpful to your fishkeeping journey.

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2018-09-24T17:55:00+00:00

10 Comments

  1. Koach May 5, 2017 at 6:33 pm - Reply

    I have had my new 55 gallon tank up and running for 4+ weeks. I am going to be moving my three large comets from a poorly managed 14g hex to the new aquarium when it is done cycling. I inoculated the filter with bacteria from the hex, and allowed it to run for a week before adding the doomed feeder fish. Of 5 fish (who were very small…) the only one still alive is the largest comet, and he seems to be thriving! I came in late on the ammonia testing, and it has always been ‘ideal” according to the kit. I have live plants in the tank also, who also seem to be doing well aside from some diatom spots. I will also add that I have a Fluval 406 (100g) and a bubble wall powered by a whisper 100. The sacrificial fish loves to swim in the incoming water flow and play in the bubble wall and is very active and shows no signs of stress or disease. Does it sound safe to add my big boys? The ph is 7.5…..

    • Pure Goldfish
      Pure Goldfish May 14, 2017 at 8:35 pm - Reply

      Did you check nitrites? If you inoculated it that would speed up the cycle.

  2. New Girl June 21, 2017 at 3:23 am - Reply

    I need help! Totally new to “the cycle”. Goldfish rescue! Any help greatly appreciated!

    • Pure Goldfish
      Pure Goldfish June 24, 2017 at 9:18 pm - Reply

      What do you need help understanding?

  3. Concerned Aquarist June 27, 2017 at 3:50 am - Reply

    Decent starter article on tank cycling! Definitely recommend removing the part about using live fish to cycle a tank. Very glad you pointed out the danger to the fish, and dedicated work required to change the water everyday. Very stressful for fish.

    Also, if not wanting to keep ammonia around due to safety concerns, it is possible to ‘feed’ the tank with fish food every few days to decay and create ammonia naturally. This would be done a week in advance prior to adding bottled beneficial bacteria. You will know its working once a whitish hazy bacteria bloom occurs for a day or so after adding the bacteria.

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    • Pure Goldfish
      Pure Goldfish June 28, 2017 at 4:14 pm - Reply

      Thanks for the tips; it’s definitely time to revisit this article and make some updates 🙂

  4. Darcy February 5, 2018 at 9:53 pm - Reply

    I added my goldfish (2 comet ) to a new tank (20 gal) before learning about “cycling”. As soon as I discovered this, I purchased a test kit and have been changing the water frequently and adding bacteria. No ammonia showing for over 2 weeks. Two days ago my ammonia was up to 1 ppm, so I did a 70% water change. Today I did a 25% water change and it is down to: ammonia= .25ppm, nitrites=.25ppm and nitrates are showing up at 5 ppm. This is the first time I have seen nitrates in the tank. Does this sound normal? Any suggestions, should I continue to do water changes to keep ammonia and nitrites down? How low without robbing the bacteria of food?

    Rating: 5
    • Pure Goldfish
      Pure Goldfish February 11, 2018 at 9:59 pm - Reply

      Nitrates should show up as the cycling progresses, but the ammonia needs to be steadily at 0 to be considered cycled. Just let its run its course, introduce ammonia regularly to feed the bacteria.

  5. brenden April 25, 2018 at 3:27 pm - Reply

    im going buy a ten gallon and a filter and feeder goldfish all at the same time how long will it take to cycle

    Rating: 3.5
    • Pure Goldfish
      Pure Goldfish April 29, 2018 at 9:56 pm - Reply

      I recommend not using a feeder to cycle. They harbor a lot of disease. A fish in cycle takes about as long as a fishless one, typically 3-4 weeks.

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