The Nitrogen Cycle of Aquariums

What is “cycling”?

A question you will hear when trying to buy fish is if your tank is cycled. This refers to the Nitrogen Cycle, an essential process of your tank where beneficial bacteria in your tank, also known as its biofilter, break down ammonia and nitrites to into nitrates.

Here’s how this cycle works:

Step 1: Fish waste, excess food, and decaying matter break down in the tank to produce ammonia. Ammonia is very toxic to fish and will lead to fish death if left unchecked.

Step 2: Nitrosomonas, a type of beneficial bacteria, will eat the ammonia and produce nitrites. Nitrites are just as toxic to fish as ammonia is.

Step 3: Nitrobacter, another type of beneficial bacteria, then eat the nitrites and produce nitrates. Nitrates are not as toxic to fish as ammonia and nitrites are, but can be harmful if left to reach large amounts.

Step 4: Water changes and live aquarium plants are used to remove nitrates. There are products that can help remove nitrates, such as Seachem’s de❊nitrate as an example, for cases where water changes and live plants aren’t enough or easily possible to do.

 

How can I start a tank’s cycle?

The main thing needed to even start a tank’s nitrogen cycle is a source of ammonia.  The beneficial bacteria in the tank aren’t able to grow and propagate if they don’t have any food source.  Remember with whatever method you decide to use to add a dechlorinator. Seachem’s Prime or Aquarium Co-op’s Easy Dechlorinator for example, to your tank water, since chlorine will kill the bacteria you are trying to grow.

 

With Fish

With this method of starting a cycle, you are making use of a fish’s waste to provide the ammonia to start a cycle. This is generally considered a common method, but it is stressful to the fish used. Constant monitoring and maintenance of the tank will be necessary.

If going this route:

· Find out which fish of your planned fish for the tank is the hardiest and most durable of the bunch. This would be the fish you will use for a fish-in method.  If none of the fish you intend to keep in the tank are particularly hardy, then this is likely not a method you should use.

· Start out with a very, very small amount of fish. One small fish per 10 gallons of water is a generally suggested amount.

· Feed the fish very lightly, gradually increasing the amount of food given over four to six weeks to eventually reach regular food levels. Excess food is an additional source of ammonia, thus overfeeding should be avoided at all costs.

· Test ammonia and nitrite levels daily. If there is any detectable amounts of ammonia or nitrite in the tank(0.2 parts per million(ppm) or higher), do a partial water change to remove the toxic compounds and provide new clean water for your fish. Detectable levels of ammonia or nitrate means there is not enough beneficial bacteria in your tank to process your fish’s waste, so your cycle is still being established.

· The tank is considered cycled when you are able to feed your fish normal amounts of food for a week, the levels of ammonia and nitrite stay at 0 ppm, and your levels of nitrates are above 0 ppm. At this point, if you wish to add more fish, do so gradually so as to make sure the biofilter is able to keep up with generated fish waste.

Since this method involves the fish in the tank being under stressful water conditions until the biofilter is properly established, it has fallen out of favor due to being considered by many as cruel to the fish when alternate methods of cycling a tank are available. Even with hardier fish, this method has the risk of the fish used ending up with permanent health complications and possibly dying before the cycle is even established.

 

Fish-less

Quite a few options exist for ammonia sources other than fish waste, such as:

1. Fish Food – Also known as Ghost Feeding, this is done by adding a little bit of fish food to the tank.  As the food decomposes, it creates a source of ammonia for beneficial bacteria to feed off and start your tank’s cycle with.
2. Raw Fish  - Buying raw fish or shrimp and placing some in your tank acts a source of decaying matter in a tank, releasing ammonia as it breaks down. A 2 inch by 1 inch chunk of raw fish or a single raw shrimp at max should provide enough ammonia to start out the tank as it decays, so not much is needed.
3. 100% Ammonia – Pure Ammonia, often sold as Ammonium Chloride, can be added sparingly to a fresh tank to provide ammonia to feed growing beneficial bacteria. This method is liked for fish-less cycling due to allowing measurable consistency:

◦         Enough should be added for the tank’s ammonia levels to read as 2-4ppm, keeping in mind how much ammonia was added to reach those levels.

◦         Check every few days and keep an eye on ammonia levels, and start check nitrite levels once ammonia levels start dropping. Add ammonia to get back to 2-4ppm when levels drop to 0.5-1ppm.

◦         Start checking nitrates when nitrites start getting high, doing partial water changes when nitrite or nitrate levels get too high to properly read with your testing kit.

◦         When a test shows 0ppm ammonia and 0ppm nitrites, add ammonia until it reaches 4 ppm again and retest in 24 hours. If the levels for both drop down to 0 ppm again within that time, your tank is cycled. After this point, adding enough ammonia to reach 1 ppm daily is enough to keep the bacteria alive until you are ready to add fish.

◦         When you’re ready to add fish, check your tank’s nitrate levels to make sure they are below 20ppm. If the nitrates are higher than that, do water changes to get nitrate levels down to 20ppm or lower the day before you intend to add fish.

 

With Plants

A well-planted tank allows for a quicker establishment of a cycle by providing more area for beneficial bacteria to settle as well as live plants usually already having small colonies of beneficial bacteria “hitchhiking” on their surface. Plants also can consume nitrogen waste more effectively than bacteria, according to some studies. A fresh tank can immediately take live plants, and instead of cycling a bare tank, focus can be put on taking care of the plants in the tank via good light, substrate, and fertilizers. When the plants in the tank are showing new growth, your cycle should be good to go, with the plants absorbing ammonia and nitrates to grow new roots and leaves. Of course, beneficial bacteria in the tank still do help, but the plants in the tank act as buffers for ammonia absorption and an alternate means of getting rid of nitrates aside from water changes.

 

What helps to speed up cycling?

Seeded Material

Seeded material refers to substrate or filter media from an established tank. Since beneficial bacteria in a tank will settle on any surface that can in a tank, adding seeded material to a tank is introducing a stash of beneficial bacteria to the new tank. Having a larger amount of bacteria to start with means your biofilter will reach the amount needed for a stable cycle more quickly. However, keep in mind where you source your seeded material!  Whatever was in the tank that substrate or filter media was from is now in your fresh tank as well. For example, if the tank your seeding material came from was using copper to medicate, now copper’s in your tank, so no invertebrates for you!

 

Bacteria Starters

Exactly what it sounds like, these are literally beneficial bacteria in a bottle, a good option to use as an alternative to or alongside seeded material. Various companies offer products that include beneficial bacterial. Examples include Fritzzyme 7, its 15 times more concentrated alternative of Fritzzyme Turbostart 700, Dr. Tim’s One and Only, API Quickstart, Tetra Safestart Plus, and Seachem’s Stability, notable in that it uses spore bacteria instead of live bacteria, which allow for longer shelf stability.

 

Heat

Upping your tank’s temperature to 77-86°F puts it in temperatures where nitrifying bacteria thrive, allowing them to process ammonia and nitrites faster and finish cycling more quickly. Do not do this if fish are already in your tank, since the higher end temperatures can be considered a little too toasty for tropical fish. 76-78°F is considered comfortable for most tropical fish, but still a good temperature for aiding in cycling.

 

How long will cycling take?

Time completely depends on what is done to cycle the tank. The average time to cycle a tank is from 2 to 8 weeks. Factors that can affect this time include:

· How the tank was cycled. Fish-in usually goes faster, but at the cost of stressing the fish used.

· Any starters or seeded media added. The more of either added, the shorter the cycle time, even being able to push cycle times to as short as a day.

· The temperature of the tank. Heat makes cycling faster.

· How large the tank is. A larger tank will usually take longer to cycle.

· How often water changes are done. While water changes dilute toxins, they slow bacterial growth.

How often the tank is cleaned. While establishing a cycle, generally the tank and filters should be cleaned sparingly, or not at all if possible. Beneficial bacterial will establish itself on any surface available in your tank, so cleaning the tank removes bacteria and makes cycling take longer.