Probably the single most important step to setting up a new aquarium or fish tank is to cycle the tank before adding any fish or livestock. Like many people, when I first started keeping fish I was woefully unaware of the need to cycle an aquarium and the beneficial bacteria in an established aquarium. I knew I had to add water conditioner and do water changes but not why this was necessary.

Now, quite a few years and a lot of research later, I have become much more informed on cycling a tank. Cycling creates an environment that is rich in beneficial bacteria and a provides a high quality habitat for the fish and other livestock in an aquarium.

Cycling an aquarium, either through a Fish-in Cycle or by using a Fishless Cycle, greatly increases the chances that any fish you put into the aquarium will survive and ensures better long term health for the fish and the aquarium as a whole.

Basics of an Aquarium Cycle

The whole idea of cycling an aquarium is to provide a self-sustaining way to reduce harmful waste products that can build up and cause health issues and a low quality habitat for inhabitants in an aquarium. In nature, the solution to waste products is the Nitrogen Cycle. The Nitrogen Cycle is a process where ammonia produced by fish waste and decomposing food and organic matter is converted by bacteria, plants, and algae into Nitrite and then to Nitrate, a compound that is less toxic to aquatic animals. This same system can be created in an aquarium to ensure that the habitat provided is safe and comfortable

Components of the Nitrogen Cycle

There are three main components of the Nitrogen Cycle that come into play in an aquarium:

Ammonia (NH3)

Enters an aquarium primarily through waste from fish living in the tank and the decomposition of organic matter such as fish food, plant matter, and microorganisms. Ammonia is very toxic to fish and can be lethal if present in too high a concentration in an aquarium. Very small concentrations can can cause illness and permanent damage while concentrations of about 0.5 parts per million (PPM) or greater can kill fish quite quickly. The goal is to have 0 PPM (or as close as possible) of Ammonia in an aquarium.

Ammonia is the cause of many unpleasant effects on fish, symptoms of Ammonia poisoning including:

  • Respiratory Issues
  • Erratic swimming, darting around the tank, excitability, and odd twitching as the nerves become damaged
  • Internal and external bleeding that causes reddening of a fish’s skin
  • Attempting to escape the water by jumping out
  • Hyper-production of mucus on the skin and eyes causing visible white clouding on both the skin and eyes
  • If left untreated, death


Nitrite (NO2)

Nitrites are produced when ‘nitrosomonas’, a type of bacteria, feed on Ammonia and produce Nitrites as a waste byproduct. While not as toxic as Ammonia, Nitrite is still quite toxic to aquatic animals causing stress and eventually death with exposure. Concentrations of 0.5 PPM result in stress to fish while concentrations of 10+ PPM are lethal in a fairly short time.

Nitrites cause damage to fish by binding with the blood and preventing oxygen from being absorbed and used by the body. Symptoms of Nitrite Poisoning include:

  • Lethargy and erratic swimming
  • Brown streaks on the skin, fins, and tail
  • Raw or damaged tissue
  • Infections resulting from damage such as recurring bacterial infections
  • If left untreated, death


Nitrates (NO3)

Nitrates are the end product of the Nitrogen Cycle in an aquarium, when “nitrobacter” bacteria feed on the Nitrite and convert it into Nitrates. Nitrates are much less toxic to aquarium livestock than Ammonia and Nitrites but can still cause problems if left unchecked. Nitrate poisoning happens when fish are exposed to gradually increasing nitrate levels over a period of time. Opinions vary on what levels of Nitrate are safe in an aquarium. Generally below 40 PPM is considered safe but the lower the concentration the better.

Symptoms of Nitrate Poisoning include:

  • Lethargy and erratic swimming
  • Loss of equilibrium or swimming at strange angles and directions
  • Slow movement or becoming listless
  • Laying at the bottom of a tank
  • Rapid “breathing” or gill movement
  • In advance stages, a fish’s body may curl or become clenched
  • With exposure over time to high enough concentrations, death


Cycling Methods

There are two widely used methods to cycling an aquarium, fish-in cycling and fishless cycling.

What is Fish-In Cycling?

Fish-in cycling uses a small number of hardy fish to produce Ammonia, the source of food for the beneficial bacteria. It does allow the addition of fish right out of the gate but it does have a number of drawbacks. Cycling an aquarium creates very toxic levels of Ammonia and Nitrite into the tank that can permanently damage or kill the fish used. It is very hard on this environment is very hard on fish and can be inhumane to keep them in these conditions for weeks on end. It also has the disadvantage of being slower and less precise – it can take months to cycle using this method and has a higher chance of crashing or stalling, forcing a restart or the death of the fish.


What is Fishless Cycling?

Fishless cycling is a fast, efficient, and more humane way to cycle your aquarium and ensure it is safe for inhabitants. Unlike fish-in cycling, fishless cycling relies on adding pure ammonia in liquid form as a source of food for the beneficial bacteria. It has the advantage of being faster than fish-in cycling, often taking 3-6 weeks. It is also more precise and efficient, and doesn’t expose fish to the toxicity created by high levels of Ammonia and Nitrite in the water.


It is recommended that you use the Fishless Cycling Method if at all possible.


What Do You Need for a Fishless Cycle?

There are a few basic items you need to complete a fishless cycle. In addition to the aquarium you wish to cycle and a filter (whatever type you choose – canister, hang on back, sponge) you will need the following items:

  1. Ammonia – You want to purchase a bottle of pure ammonia, one without scents, detergents, soaps, or additives of any kind. This is very important as any additives can cause issues with both your cycle and any inhabitants added after the cycle is complete. Strength of ammonia (5%, 10% etc.) doesn’t matter, you can compensate by adjusting the amount you add.
  2. Test Kit – You need to track how much Ammonia, Nitrite, and Nitrate to know where the cycle is and when to add more Ammonia or do a water change to reduce Nitrates. I use the API Freshwater Master Test Kit, it is generally accepted that liquid test kits are more accurate than test strips and once you get some practice it is very easy and quick to test the water and get the results.
  3. Water Dechlorinator –  Any water conditioner that removes chlorine/chloramine in the water (these are added to water supplies to specifically kill off bacteria) will do.
  4. Syringe – Used for dosing specific amounts of Ammonia to get the required concentrations for optimal bacteria growth. I like syringes better than pipettes or small containers as it is easier to measure out specific amounts.
  5. Air Pump / Air Stone / Air Line – While not absolutely necessary for cycling having an air stone to introduce more oxygen into the water will greatly speed up the time needed to cycle.
  6. Heater – Again while not necessary, the bacteria you are trying to grow thrive at temperatures between 25-30 C (77-86F) and warmer temperatures will help them reproduce faster, decreasing the time it takes to complete the cycle.
  7. Fish Food – Adding a small amount of fish food will introduce nutrients that will help the beneficial bacteria grow.
  8. Notebook – Writing down the water test results will help you monitor and track the progress of your cycle.
  9. Established Media – if you can find someone willing to give you a sponge, filter floss, bioballs,  ceramic rings, or any other kind of filter media that has been in an established tank grab it; it will greatly reduce the time it takes to cycle your tank.

Bacteria in a Bottle

Itis a matter of personal opinion on whether or not to use products designed to add beneficial bacteria or help speed up an aquarium cycle. Personally, I’m wary of any of these claims. It seems questionable whether bacteria could survive sitting on a shelf for any extended period of time. I don’t use any of these products but I won’t say they don’t help as I don’t know for sure. If you wish to try using them by all means add them to your tank at the start of the cycling process. There are reports that adding these products can result in odd readings on your test kit so be aware of this and keep and eye out.


Plants While Cycling

Yes! Plants will thrive in the Ammonia and Nitrate rich environment during a fishless cycle. In fact, plants taken from an established tank will have some beneficial bacteria on them that will help the process get started. Plants will add visual interest while you wait for the cycle to complete and the addition of fish. Ensure the lighting level is at an intensity that is just enough for your plants to grow, too much will result in algae that will compete for the Ammonia and Nitrates .

Steps to Fishless Cycle and Aquarium

  1. Set up your aquarium. Fill it up with water (make sure you dechlorinate with your water conditioner according to the directions), then setup and plug in any filters, heaters, air pumps, and air stones and ensure they are working properly. Add any established media to the filter or aquarium. Any live plants can be added at this point as well.
  2. Turn up your heater get the water temperature between 25-30C (77-86F). This temperature range is where beneficial bacteria thrive and reproduce the fastest.
  3. Turn up the the air stone to max! More bubbles are better – they introduce needed oxygen into the water. If you don’t have an air stone try lowering the water level so the filter output splashes onto the water’s surface. Surface agitation increases the amount of oxygen able to dissolve into the water.
  4. Add in your Ammonia. You want to aim for a concentration of 4-5 PPM. Use this Ammonia Calculator to determine how much Ammonia to add. If you accidentally add too much, you can do a water change to reduce the concentration.
  5. Add a tiny bit of finely ground up fish food to add nutrients and phosphates into the water that help bacteria grow.
  6. Now wait. Test the Ammonia level every day or every couple days at most. When the concentration begins to drop the cycle has started. Let it drop to about 1 PPM and then dose enough Ammonia to raise the total concentration back up to 4 PPM. Don’t let it drop to zero, this will starve the bacteria and potentially stall the cycle.
  7. Once the Ammonia level starts dropping, start testing for NitrItes. It is normal for there to be a delay of several days between the time Ammonia drops and NitrItes begin to show on the test kit.
  8. Every time the Ammonia drops to around 1 PPM add enough to get it back up to around the 4-5 PPM level.As the cycle continues the time it takes for the bacteria to use the available Ammonia will decrease from a week, to several days, to a day or matter of hours.
  9. Keep testing your Nitrite levels. Once it show midway on your test kit, start testing for Nitrates. Once Nitrates are detected using the test kit, the cycle is well underway.
  10. An important part of the cycle at this point is to ensure that Nitrite and Nitrate levels don’t get too high. This can stall the cycle and potentially kill off the bacteria that are growing. When your levels reach around 5 PPM for Nitrites or 100 PPM for Nitrates – do a 75% water change. This will bring the levels back to a healthy level and ensure your cycle continues smoothly. Keep testing and doing water changes as needed to keep Nitrite levels around 2-3 PPM and Nitrate levels below 40 PPM.
  11. Keep testing and adding Ammonia to keep concentrations at 4-5 PPM.
  12. Eventually test will begin to show 0 PPM Ammonia and 0 PPM Nitrites with high levels of Nitrates. This means that technically the cycle is complete! Just to make sure, it is good to do a final check. You want your bio-filter to be able to process Ammonia > Nitrites > Nitrates in a day. Do a water change and dose Ammonia back up to 4 PPM. Wait for around 24 hours and test for all three compounds. If you have 0 PPM Ammonia and Nitrites and higher levels of Nitrates the cycle is complete!
  13. You can add fish at this point! If it is going to be a few days before any livestock is added you should dose around 1 PPM of Ammonia daily to keep the bacteria alive.
  14. A day or so before you plan on adding fish, there two important things to do. First, turn the heater down to the appropriate temperature for the fish being added. Second, perform a HUGE water change –  around 90%. The Nitrates will have built up like crazy during the cycle and you’ve got reduce them to a safe level for fish. The lower the better.
  15. Finally, add fish! The bio-filter is so strong that you could technically add the full stocking level to your tank, but you don’t necessarily want to. If you add too many at first you could overwhelm the system , but if you only add a few tiny fish at the beginning they won’t provide enough Ammonia to keep the beneficial bacteria alive. Shoot for a middle ground and add a reasonable amount of fish depending on your tank size and and the types of fish you are keeping.

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