The Nitrogen Cycle and New Tank Syndrome
The nitrogen cycle as it pertains to the home aquarium is the process of establishing beneficial bacteria in order to break down nitrogenous waste compounds into less harmful nitrates that can be removed from the aquarium via plants or water changes.
Food in equals waste out
Like all living creatures, fish give off waste products, these nitrogenous waste products break down into ammonia (NH3), which is highly toxic to both fish & Invertebrates. In nature, the volume of water per fish is extremely high and waste products become diluted to low concentrations and are ultimately purified by the mass amounts of nitrofying bacteria that exist. In aquariums, however, it can take as little as a few hours for ammonia concentrations to reach toxic levels. How much ammonia is too much? The quick answer is: if a test kit is able to measure it, you’ve got too much, it’s in a high enough concentrations to stress fish and cause irritation. Consider emergency action such as water changes using Reverse Osmosed water or ammonia locking products, if your ammonia levels are .25ppm or higher.
What Is the Nitrogen Cycle?
The Nitrogen Cycle is the biological process that converts ammonia into other, relatively harmless nitrogen compounds. Fortunately, several species of bacteria do this conversion for us. Some species convert ammonia (NH3) to nitrite (N02-), while others convert nitrite to nitrate (NO3-). Thus, cycling the tank refers to the process of establishing bacterial colonies in the filter bed that convert ammonia -> nitrite -> nitrate. Nitrate is only toxic at high levels that take time to accumulate and can be removed through partial water changes or aquatic plant life.
The desired species of nitrifying bacteria are present everywhere (e.g., in the air), therefore, once you have an ammonia source in your tank, its only a matter of time before the desired bacteria establish a colony in your filter bed. The most common way to do this is to seed your new aquarium using water or substrate from and existing aquarium, live rock or to place one or two (emphasis on one or two) hardy and inexpensive fish in your aquarium (damselfish and chromis are good for this purpose). The fish waste contains the ammonia on which the bacteria will live and grow, be careful not to overfeed them, causing more ammonia than can be handled by the growing bacteria bed.
New Tank Syndrome
During the cycling process, ammonia levels will vary wildly as the nitrite-forming bacteria take hold. Because nitrate-forming bacteria don’t even begin to appear until nitrite is present in significant quantities, nitrite levels skyrocket (as the built-up ammonia is converted), continuing to rise as the continually-produced ammonia is converted to nitrite. Once the nitrate-forming bacteria take hold, nitrite levels fall, nitrate levels rise, and the tank is fully cycled.
When is a new tank ready for fish?
Your tank is fully cycled once nitrates are being produced (and ammonia and nitrite levels are zero). To determine when the cycle has completed, you will need to have a marine water test kit, and measure the levels weekly at first and then monthly. Another possibility is to bring water samples to your local fish store and let them perform the test for you. The cycling process normally takes anywhere from 2-6 weeks, at temperatures below 70F it takes even longer to cycle a tank. In comparison to other types of bacteria, nitrifying bacteria grow slowly. Under optimal conditions; however, it can take only 15 hours for a colony to double in size! It is possible to speed up the cycling process by using bacteria based products available that will speed the process of building the nitrifying bacteria beds. The use of these products along with proper temperature, water flow and lighting can shorten the cycling process to 1-3 weeks. Reverse Osmose water should be used to limit the amount of ammonia, nitrite and silicates that are present in the water.
Don’t Rush It!
Warning: AVOID THE TEMPTATION TO GET MORE FISH UNTIL AFTER YOUR TANK HAS FULLY CYCLED! More fish means more ammonia production, increasing the stress on all fish and the likelihood of fish deaths. Once ammonia levels reach highly stressful or toxic levels, your tank has succumbed to New Tank Syndrome; the tank has not yet fully cycled, and the accumulating ammonia has concentrations lethal to your fish. Each time you add a couple of fish you will need to allow a couple of weeks for the bacteria in your aquarium filter bed to grow in number to handle the increased amount of ammonia and filtering loads. Keep in mind that not only are you adding more fish, but you are also increasing the amount of food fed, consumed and the amount of uneated food, all of which creates higher ammonia levels.
How Much Ammonia Is Too Much?
In an established tank ammonia levels should always be 0 ppm, which is undetectable using standard test kits available at stores. The presence of detectable levels indicates that your bio filter is not working adequately, either because your tank has not yet been completely cycled, or the filter is not functioning adequately (e.g. too small for fish load, clogged, etc.) It is imperative that you address the cause of the problem (filter) in addition to the symptoms (high ammonia levels).
The exact concentration at which ammonia becomes toxic to fish varies among species; some are more tolerant than others. In addition, other factors like water temperature and chemistry play a significant role. For example, ammonia (NH3) continually changes to ammonium (NH4+) and vice versa, with the relative concentrations of each depending on the water’s temperature and pH. Ammonia is extremely toxic; ammonium is relatively harmless. At higher temperatures and pH, more of the nitrogen is in the toxic ammonia form than at lower pH.
Speeding Up Cycling Time
The nitrogen cycle can be sped up or jump started in a number of ways. Unfortunately, they require access to an established tank, which a beginning aquarist may not have available. The basic idea is to find an established tank, take some of the bacteria out of it and place them in the new tank. Most filters have some sort of foam block or floss insert on which nitrifying bacteria attach. Borrowing all or part of such an insert and placing it in the new tanks filter gets things going more quickly. If the established tank uses an undergravel filter, nitrifying bacteria will be attached to the gravel. Take some of the gravel (a cup or more) and hang it in a mesh bag in your filter (if you can), or lay it over the top of the gravel in the new tank (if it has an UGF).
More recently, products containing colonies of nitrifying bacteria have become available at pet shops (e.g. Fritz, Bio-zyme, Cycle). In theory, adding the bacteria jump-starts the colonization process as above. Net experience with such products has been mixed; some folks report success, while others report they don’t work as well as advertised. In principle, such products should work well. However, nitrifying bacteria cannot live indefinitely without oxygen and food. Thus, the effectiveness of a product depends on its freshness and can be adversely effected by poor handling (e.g. overheating). Unfortunately, these products dont come with a freshness date, so there is no way to know how old they are.
Of course, there are many variations on the above that work. However, it is a bit difficult to give an exact recipe that is guaranteed to work. It is advisable to take a conservative approach and not add fish too quickly. In addition, testing the water to be sure nitrates are being produced eliminates the guesswork of determining when your tank has cycled. Remember that using any method to cycle your tank is going to take some time and that following the advice written here along with some patience and diligent water testing, will in the end result in a well established and enjoyable marine aquarium.