How to Do a Nitrogen Cycle for Your Fish Tank

Let’s get started with a list of things you will need to do a nitrogen cycle for your fish tank.

Things You Need for Cycling Your Tank

Note: Any amount of water can be cycled however water tanks under 3 gallons [11.3 ltrs] can be difficult to maintain and hold their cycle. If your tank is less than 3 gal, we recommended to perform 100% water changes regularly instead of cycling.

Part I: Tank Set Up

You will need to do some tank setup before you cycle your tank. Here are the steps you need to do for setting up your tank:

Tank Set-up Steps

Step 1. Prepare your substrate: Rinse the substrate (rocks, sand, gravel, marbles and so on) and add it to your empty tank. The substrate will be home to much of the beneficial bacteria that will live in your tank. A rougher substrate like sand or gravel is recommend as it will be a better home to bacteria then smooth large rocks or marbles.

If you plan on seeding your tank with gravel from an established tank you can add it to the tank at this time.

Step 2. Fill your tank with water: Fill your tank with room temperature tap water.

Note: No fish are being added to the tank at this time so it is not necessary to add any water conditioners or ammonia neutralizers. Doing this can present inaccurate test results.

Step 3. Connecting your filter:  There are many different types of filters on the market and the type you choose  will depend on the following:

  • Tank Size
  • Bioload (amount of fish waster)
  • Personal preference

A power filter comes with a bio-wheel, this is nice as it provides additional surface area for beneficial bacteria to live on. The filter media will house the majority

The filter media itself will house the bulk of all the beneficial bacteria in your tank.

Note: You do not want to cycle a tank without a filter . You also do not want to keep a filter in an aquarium that you do not intend to cycle. (i.e. 100% water changes instead) Doing this will force your tank to constantly cycle exposing your fish to toxins over and over.

Note: If you plan on using filter media from an established tank, add it at this time. Seeding is not needed as thee bacteria you will be culturing is already present in your tank. When adding established filter media, this may dramatically reduce the time needed to fully cycle your tank.

Step 4. Amount of tubing you will need:  You will need to measure out the amount of tubing you will need for the air-stone to reach from the bottom of your tank to your air pump.

Make sure you connect a reverse flow valve as this will ensure that your pump will not accidentally siphon water out of your tank in the event of a power outage.

This valve is not expensive and can be found at any pet or fish store near the air stones.

Attach the air-stone to the tube and place it in your tank . Surface breathing fish like Bettas don’t require much dissolved oxygen in the water, however the beneficial bacteria you are cultivating will love it.

Step 5. Testing your tank water:  Now that your tank is all set up it’s a good idea to run the gambit of tests to see what your water parameters are fresh out of the tap without any additives. Record these results. You may find there is already some ammonia present. It is quite common to find up to 0.5 ppm or greater in your tap water.

Part II: The Nitrogen Cycle (Biological Cycle)

In this section we cover the steps to do a nitrogen cycle also known as a biological cycle.


Nitrogen Cycle Steps

Cycling with fish – When you cycle your tank with fish in it they produce the ammonia needed for the bacteria to consume. So there is no need to add ammonia to the water when cycling. However in this case we are cycling without fish in the tank.

Cycling without fish – When cycling without fish we will need to provide the ammonia that is needed to sustain and encourage the growth of beneficial bacteria.

Note: Ammonia can be found at your grocery or hardware store. Make sure the ammonia only has ammonia hydroxide and water. Some have detergents and coloring added to it make sure you do not get these forms of ammonia.

Step 1: Adding ammonia to your tank –  Depending on the brand of ammonia will effect the potency of ammonia hydroxide this makes it so there is no exact quantity to add to your tank water.

You will need to use trial and error to determine how much ammonia to add to your tank water.

Start with adding about 3 – 5 drops per gallon of water, you can add more if you need it. However it is much harder to remove the ammonia if you add too much. Allow this to mix for a few minutes and then test the ammonia levels with your salicylate ammonia test kit.

Note: You will want to add enough ammonia to simulate the bio-load your tank will have once you add fish to it. For a simple tank setup this is usually around 2.0 ppm.

Once you have tested your water, add enough ammonia to bring the levels up to the 2.0 ppm. A little over the 2.0 ppm is ok. Retest your ammonia level and record your results.

Step 2: Maintain your ammonia levels – Things you need to do to maintain healthy tank water.

  • Everyday add enough ammonia to keep the ammonia levels at about 2.0 ppm
  • Test your ammonia, nitrite and nitrate each day
  • Record your test results
  • Check your pH levels – Any sudden drop or rise in pH can cause your beneficial bacteria to die off and slow or halt your progress.

Over the next 1 – 2 weeks the beneficial bacteria will consume ammonia and begin to break down the ammonia you have been adding. The bacteria will continue to multiply to meet the demand. The bacteria will give off nitrite as a byproduct and this will start to show up on your tests. Once this happens you will know the cycle is well under way.

Step 3: Cycle Progression –  At the point your tests will be showing nitrite levels are beginning to raise and you can cut the amount of ammonia you add each day by half. As ammonia-consuming bacteria multiply, you will see the ammonia levels drop and nitrite levels rise.

A second type of beneficial bacteria that lives in your tank will consume harmful nitrite and give off less harmful nitrate as a byproduct. With this second type of bacteria, you will see the nitrite levels drop and the nitrate levels rise. This usually occurs around the weeks 3 – 4 mark.

When the ammonia levels fall back to zero,  the nitrite levels fall back to zero and the nitrate levels are showing on your tests. then and only then, is your tank completely cycled.

Step 4: Partial water change – You will want to do a partial water change to keep nitrates at a safe level. You want the nitrates to be around 10 – 20 ppm.

After this water change treat your water with a conditioner that neutralizes:

  • Chlorine
  • Chloramines
  • Heavy metals

Then acclimate your fish to their tank. If you don’t have fish right away, be sure to keep adding ammonia daily to keep the cycle going until you are ready to add fish to your tank.

Step 5:  Maintain a safe environment –

  • Make sure to do partial 25% water changes each week to keep the nitrate levels in the safe range.
  • You will want to occasionally, test your water for ammonia & nitrite to make sure the cycle is continuing.
  • Nitrate and pH tests should be performed weekly.

Once your tank is cycled it can stay cycled for many years with proper maintenance.

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