Nitrogen Cycle

What is Needed for Tank Cycling

  • Tank
  • Filter & Filter Media
  • Air-stone
  • Air-pump
  • Reverse-flow Valve
  • Tubing
  • Substrate
  • Pure Ammonia
  • Eye Dropper
  • Salicylate Ammonia Test Kit
  • PH Test Kit
  • Pen & Paper

Optional

  • Filter media or gravel from an established tank.

Any amount of water can be cycled but volumes under 3 gallons [11.3 ltrs] can be difficult to maintain and hold their cycle. If your tank is less than 3 gal, it’s recommended to perform 100% water changes regularly instead of cycling.

Part I: Tank Set Up

Photo by: Shuffleart

Betta Fish Photo by: Shuffleart

1. Rinse the substrate and add it to your empty tank. This substrate will house much of the beneficial bacteria that will live in your tank. A rougher substrate like sand or gravel 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 add it to the tank at this time.

2. Fill your tank with room temperature tap water. Since no fish are being added at this time it is not necessary to add any water conditioners or ammonia neutralizers. Doing so could present inaccurate results.

3. Connect your filter. There are many different types of filters on the market and the type you choose depends on the tank size, bioload (or amount of fish waste) and personal preference. Power filters that come with a bio-wheel are nice because the wheel provides additional surface area for beneficial bacteria to cling. The filter media itself will house the majority of all the beneficial bacteria in your tank. You do not want to cycle a tank without a filter nor do you want to keep a filter in an aquarium that you do not intend to cycle. (i.e. 100% water changes instead) Doing so will force your tank to perpetually cycle exposing your fish to toxins repeatedly.

If you plan on using filter media from an established tank, add it at this time. The bacteria you will be culturing is already present in your tank so seeding isn’t needed. Adding the established filter media, however, may dramatically decrease the total time needed to fully cycle your tank.

4. Measure out the amount of tubing you’ll need for the air-stone to reach from the bottom of your tank to the air pump. Connecting the reverse flow valve will ensure that your pump will not accidentally begin siphoning water out of your tank in the event of a power outage. This valve is very inexpensive and can be found near the air stones in most fish stores. Attach the air-stone and place it in your tank. Even though Anabantoids (surface breathing fish) like Bettas don’t require much dissolved oxygen in the water, the beneficial bacteria you are developing will.

5. 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 (aka the Biological Cycle)

Planted Aquarium Photo by: Nat Tarbox

Planted Aquarium Photo by: Nat Tarbox

1. When cycling with fish it is the fish themselves that excrete ammonia which is consumed by the bacteria, but since we are cycling without fish it’s up to us to provide enough ammonia to sustain and encourage growth of the bacteria. Ammonia can be purchased from a grocery store or hardware store. Be sure to check that the ingredients are solely ammonia hydroxide and water. Be sure there are no detergents or artificial colors added to the bottle. If you are unsure, shake the bottle gently. Suds will appear if detergents are present. Ammonia chloride is an even better choice for tank cycling because it is less likely to effect the pH but it can be much more difficult to find. Check your LFS to see if they carry ammonia chloride.

2. The potency of ammonia hydroxide depends on the brand you buy and there is no exact quantity to add to your tank water. Unfortunately, trial and error is the only way to determine how much to add. Begin by adding about 3 – 5 drops per gallon of water, allow it to mix for a few minutes and then test your ammonia levels with your salicylate ammonia test kit. You will ultimately want to add enough ammonia to equal the potential bioload. For most simple tank set ups, an ammonia level of about 2.0 ppm will suffice. After testing your water, add enough ammonia to bring it up to the 2.0 ppm level. If it goes a little over that is ok. Retest your ammonia level and record your results.

3. Each day, add enough ammonia to keep the level at about 2.0 ppm. Test your tank for ammonia, nitrite and nitrate each day. Record your results after each test. Check your pH often as well. 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 that consume ammonia will begin to break down the ammonia you have been adding and will continue to multiply to meet the demand. Those bacteria give off nitrite as a byproduct. Once nitrite begins showing on your tests you’ll know the cycle is well under way.

4. At the point your tests show nitrite levels beginning to raise 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 then themselves, give off less harmful nitrate as a byproduct.

5. Because of this second type of bacteria, you will then see the nitrite levels drop and the nitrate levels begin to rise. This usually occurs around weeks 3 – 4.

6. Once 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. Congratulations!

7. At this point you will want to do a partial water change to keep nitrates at a safe level. Usually around 10 – 20 ppm is fine. After this water change treat your water with a conditioner that neutralizes chlorine, chloramines and heavy metals and acclimate your fish. If you don’t have fish right away, be sure to keep adding ammonia daily to keep the cycle going until you are ready.

8. To maintain a safe environment, do partial 25% water changes each week to keep the nitrate levels in the safe range. On occasion, it’s a good idea to test your water for ammonia & nitrite just to make sure the cycle is continuing. Nitrate and pH tests should be performed at least weekly. Once your tank is cycled it can stay cycled for many years with proper maintenance.