Nitrogen cycle or new tank syndrome or aquarium cycling:
Aquarium cycling (or Nitrogen Cycle) is the process by which useful bacteria colonise in your aquarium. These bacteria live on aquarium waste and decompose the toxic component such as Ammonium to nitrate in a two step process (Ammonia -> Nitrite -> Nitrate). The effects of the cycling process are sometimes referred to as “New Tank Syndrome”.
Aquarium being a closed environment with limited quantity of water, any kind of waste inside the aquarium can generate harmful/toxic chemicals. Air-borne bacteria living on such wastes produced by your aquarium fishes/pets, continue to grow, colonise and convert these wastes to safer by-products. However this process takes several weeks to months. Your initial fish will face this stress till the colonies of useful bacteria are established.
Nitrogen Cycle is particularly important because in a brand new aquarium, the aquarium waste continues to grow which produces toxic chemicals and the most important ones are Ammonia (NH3) & Nitrite (NO2). If the ammonia or nitrite content increases significantly (know as ammonia and nitrite spikes), it will damage the gills of your fish and can kill them. Even if your fish survive during ammonia or nitrite spikes, their gills will be damaged and they will be living in an unhealthy environment with lot of pain.
If you are a beginner then understanding the Nitrogen Cycle process will make it little easy or less painful for your aquatic pets. Before we get into details, let us understand the different types of cycling method and few basic components involved in Nitrogen cycle.
Components of Aquarium cycling:
Aquarium Waste: Anything organic that stays/is added to the aquarium and not consumed are call aquatic waste. Uneaten food, fish wastes (like pooh or urine), decaying plants, dead fish are the best example for aquarium waste. All type of aquarium wastes is very high in protein.
Nitrogen (N2): Nitrogen is part of every living tissue and comprises 78% of the atmosphere but free Nitrogen in the atmosphere is not the form that plants or animals can use.
Ammonia (NH3): When an organism dies, nitrogen moves from plant or animal into the inorganic chemical ammonia by the process of bacterial decay or Nitrification. This decomposition of animal protein (called mineralization) produces large quantities of ammonia through the process of ammonification.
Nitrite (NO2-): It’s an intermediate state in oxidation process between ammonia to nitrate and concentration in oxygenated water is typically less than 0.005 mg/l. Nitrite reduces the oxygen-carrying capacity of the blood. Anything more than 0.05 mg/l is dangerous to your fish. Some fishes are more sensitive to nitrite than others. Studies also show smaller fish are less sensitive to nitrite than bigger fish.
Nitrate (NO3-): Plants consumes nitrate and during photosynthesis converts them to nucleic acids and proteins or in other words acts as a fertilizer for plants. Nitrates are not highly toxic to fish but can affect the health of the fish if left on high concentration. Nitrate will contribute to loss of appetite and stress your fish, as well as contribute to algae growth, so it is important to do regular small water changes to keep your tank in best condition.
Let us understand different types of cycling methods:
There are primarily 4 types of Aquarium cycling:
- Cycling with starter fish: This is the most common and traditional cycling method. In this you initiate the cycle by introducing few hardy fish (referred as starter fish)
- Fish-less cycling: As the name suggests, the tank is cycled with no aquatic pets in the aquarium, but with ammonia.
- Silent cycling: In silent cycling the tank is cycled with densely planted aquatic plants.
- Cycling with chemicals: In this cycling method, the tank is cycled with commercially available chemical or products.
Cycling with starter fish:
This process is probably most simple and easy but the down side is, your starter fish (2-4 small, hardy, disposable fish that you introduce first) takes all the pain to provide a safer environment for you aquatic pets. Before you start the cycle (i.e, before introducing any new fish), leave your tank for at least a week filled with tap water – this will reduce the chlorine content of the water and also settle down any suspended particles. Then introduce only few starter fish to begin the cycle.
This cycling process has 3 stages:
Stage 1 – Primary stage (day 1 to day 3): When a fish is introduced to a new tank, they generate aquarium waste which then breaks down to either ammonium(NH4) (for water with PH < 7) or Ammonia (NH3) ( for water with PH > 7). The NH4 is not toxic but the NH3 is toxic and very harmful to the fish. The Ammonia (NH3) rises very rapidly after 48 to 72 hours from the beginning of the cycle. Anything more than 2mg/l of ammonia is dangerous for fish.
Stage 2 – Intermediate stage (day 3 to day 7): From the 3rd day onwards, the useful bacteria (called Nitrosomonas) oxidizes the ammonia to nitrite which is still toxic. Nitrosomonas are so called nitrifiers which consume ammonia and excrete nitrite.
Stage 3 – Final Stage (day 8 to day 42): After a while another set of useful bacteria (called Nitrobacter & Nitrospira) converts the nitrites into nitrates. To reduce this nitrate concentration, you need to perform regular partial water change (every week).
Note: I have read many articles and some of them argue about which bacteria (Nitrobacter or Nitrospira) actually convert nitrite into nitrate and I am not sure which one is actually responsible. However the bottom-line is one of the bacteria converts the nitrite to nitrate.
Tips: There are several ways to jumpstart your above nitrogen cycle and can reduce the cycle time.
- If you already have an aquarium, or know anyone who has, you can use mature bacteria colony from an existing cycled tank to jumpstart a new one in your new aquarium. Gravel and biological filter media is a rich source for bacteria. Keep in mind that even harmful bacteria can be included when you use gravel and filter media from another aquarium.
- Another way to jumpstart the new bacteria colony is to buy water additives with small populations of suitable bacteria from fish stores.
Recommended starter fish: Choose few hardy fish and something that you will want to have in your tank on the long run. I have seen many pet shops suggesting using feeder goldfish. Please do not cycle your tank with any goldfish unless you intend to keep goldfish. For a small community fish tank I would recommend White Clouds Mountain Minnows or Zebra Danios. They are hardy cycling fish and goes with any community tank (except tank with very big fish). You can also use Cherry Barbs or Tiger Barbs but these are slightly more aggressive.
The fishless cycle is a new cycling method and has become very popular in recent years. Fish-less cycling requires lot more effort and longer duration to complete the cycle. You need to have patience for fish-less cycling. If you are a beginner then you may find it difficult but by doing this you are not troubling any fish. In fish-less cycling, do not introduce any fish till the cycle is complete.
You will need the following items for fish less cycling
- A testing kit to test ammonia, nitrites, and nitrates.
- A bottle of pure ammonia with no other impurities (except water or ammonium hydroxide) on it. Pure liquid ammonia is clear with no bubbles or fizz on it.
- Some bacteria (know as seeders) from any other cycled tank. The bacteria colonise densely in aquarium substrate or filter media. So get some water (about 2.5 US gallon or 10 litres), some substrate/gravel/pebbles (1kg) from a cycled tank, squeezed water from the filter media. If possible get a part of filter media. More bacteria you have the faster the cycling process. If you don’t have access to a fully cycled tank then you may ask your local store to help you.
Once you have all the ingredients, you can start the cycling process as described in the following steps:
Step 1: Fill up your aquarium tank with 40 – 50% water. Don’t fill the tank 100% as you need to do a water change end of the cycle to remove any nitrate content.
Step 2: Take few gravel/substrate and filter media and make a small packet (so that it can fit into your filter) using any clean cloth. Keep the packet inside the filter.
Step 3: Add the remaining substrate/gravel to your new tank.
Step 4: As cycling depends on oxygen, start your air pump with as many air stones as you can. Leave the light and air pump till the cycle is complete.
Step 5: Increase the water temperature to 30 Degree C or 86 Degree F. Higher temperature helps the cycling process.
Step 6: Now add the pure ammonia drop by drop (and keep a count of it), test the ammonia concentration. Continue this exercise till the ammonia concentration reaches up to 5.0 ppm. Make a note of amount of ammonia drops you have added to for future reference. Remember, if you add too much of ammonia then the cycle may not start.
Step 7: Leave your aquarium for 24 hours
Step 8: Add the same amount of ammonia (amount that you have added on the day one to reach 5.0 ppm) to your tank every day and test your water till you start some nitrite reading.
Step 9: Test the water for ammonia & nitrite every day till the cycle is complete.
Step 10: Once you start getting nitrite reading reduce the ammonia dose to half and continue the process till the nitrite reduces to zero.
Step 11: This zero nitrite and ammonia represents that the useful bacteria have colonised, but the water has a high concentration of nitrate (NO3-) on it and too much nitrate is dangerous to fish so you need to do a water change.
Step 12: You can change up to 95% water (but don’t wash the filter or substrate otherwise you will loose all your bacteria. After water change test the nitrate content. If the nitrate content is still high do some more water change and test again. Continue this process till you reach the nitrate concentration less than 10 mg/l.
Step 13: Finally test the water once again and a reading with zero ammonia , zero nitrite and nitrate less than 10 gm/l represents a fully cycled tank which is safe for your aquatic pets.
Ammonia Test: you can test Ammonia from day 3 onwards on a daily basis till you see a sharp drop in the Ammonia concentration. After the sharp drop continue your test less frequently (may be once on 4-5 days) till ammonia concentration reached to Zero. If your Ammonia concentration does not drop then you will find your fish are very stressed or trying to breath from the surface of your tank. In such cases you need to take quick action to reduce the Ammonia either by partial water change (up to 50%) or ask your local fish store to provide suitable chemical for it.
Nitrites Test: You can test nitrite content after a week once in every 4 or 5 days till the concentration reduces to zero. If you find your fish are stressed then take quick action to reduce the nitrite concentration by partial water change (up to 50%).
The overall length of a fish less cycle time can vary from 2 to 6 weeks depending on temperature, PH, light, air supply and bacteria that you add to initiate the process.
In silent cycling you fill the aquarium with densely planted aquatic plants. Choose plants that are sturdy and grow fast. During a silent cycle, the levels of bacteria will typically be very low and the nitrogen will instead be consumed by the plants. This is still a comparatively unusual cycling method. According to some aquarists the plants will not only efficiently cycle the aquarium, but also decrease the spikes in nitrate and ammonia levels that are often seen during the more common cycling methods. The downside of Silent Cycling is it require a very long cycling period.
Cycling your tank using chemical:
There are many commercial chemical products which can control ammonia. Personally I would not recommend this method for home aquarium. This requires a lot of expertise and may be applicable for huge tanks. When you use any chemical to stop unwanted increase in ammonia levels often results in starvation of biological filter (remember, useful bacteria live on ammonia) and may destroy the existing colony which will lead to more ammonia problems. If the biological filter is destroyed, you will observe ammonia spike on your tank and have to cycle your tank as it’s a new setup.
As you now understand what is happening to your tank in the 1st 6 weeks of your tank setup, let me explain how to control the nitrogen cycle and make sure that the water is healthy for your fish.
Tips to control Ammonia, Nitrite, and Nitrate:
- The bacteria colonise on the filter media (sponge) so don’t replace them if it is not required. This will destroy their colony and you may see a sudden increase in nitrite/ nitrate.
- Never wash the filter media in tap water which will kill the useful bacteria. Use the tank water in a mug/pot and wash your filter media with the old aquarium water.
- Don’t try to change PH of water (if it’s not absolutely necessary) because it can be fatal for useful bacteria.
- In a planted aquarium, the aquatic plants consume ammonia & nitrates and hence contribute to the nitrogen cycle.
- If you find ammonia/nitrite/nitrate content high, check the following
— Monitor when you feed your fish, any uneaten food will generate more aquarium waste and degrade your water quality.
— Increase air circulation by volume (by adding more air-stones or increasing the running time for your air pump). Additional oxygen will help your fish to breath and speed up the oxidation process.
— For planted aquarium leave the light on for 12 hours, Plants will consume the nitrate.
— Do a partial water change up to 25%
Cooperative Institute for Research in Environmental Sciences (CIRES):
The image shown in this article on Nitrogen Cycle is from the book “The Healthy Aquarium, Author – Dr Neville Carrington” and the credit goes to the Author/publisher.