The Aquarium Nitrogen Cycle

This information presented below may be rather boring to most people, but it is absolutely essential to understand this process if you want to be successful at keeping tropical fish!

Some call it the biological cycle, the nitrification process, new tank syndrome or even the start-up cycle. They all are referring to the same cycle - The Nitrogen Cycle. This very important cycle is the establishment of beneficial bacteria in the aquarium and in the filter media that will help in the conversion of ammonia to nitrite and then the conversion of nitrite to nitrates. Check out the aquarium water chemistry page for more information on these terms.

This process can take from 2 weeks to 2 months or longer to complete. It is vital for anyone planning on keeping an aquarium with tropical fish to understand this process. Learning about this process will help you to be successful in keeping tropical fish. The best way to monitor the nitrogen cycle is to purchase a freshwater test kit or saltwater test kit that will test for ammonia, nitrites, nitrates and ph.

Test your aquarium water every other day and write down your readings. You will first see ammonia levels rising. A few weeks or so later you should see the nitrite levels rising and the ammonia levels dropping. Finally, after a few more weeks you should see the nitrate levels rising and the nitrite levels dropping. When you no longer detect ammonia or nitrites but you can detect nitrates you can assume that it is safe to add your tropical fish.

Nitrogen Cycle Stages
Stage 1
Ammonia is introduced into the aquarium via tropical fish waste and uneaten food. The tropical fish waste and excess food will break down into either ionized ammonium (NH4) or un-ionized ammonia (NH3). Ammonium is not harmful to tropical fish but ammonia is. Whether the material turns into ammonium or ammonia depends on the ph level of the water. If the ph is under 7, you will have ammonium. If the ph is 7 or higher you will have ammonia.

Stage 2
Soon, bacteria called nitrosomonas will develop and they will oxidize the ammonia in the tank, essentially eliminating it. The byproduct of ammonia oxidation is Nitrites. So we no longer have ammonia in the tank, but we now have another toxin to deal with - Nitrites. Nitrites are just as toxic to tropical fish as ammonia. If you have a test kit, you should be able to see the nitrite levels rise around the end of the first or second week.

Stage 3
Bacteria called nitrobacter will develop and they will convert the nitrites into nitrates. Nitrates are not as harmful to tropical fish as ammonia or nitrites, but nitrate is still harmful in large amounts. The quickest way to rid your aquarium of nitrates is to perform partial water changes. Once your tank is established you will need to monitor your tank water for high nitrate levels and perform partial water changes as necessary. There are other methods to control nitrates in aquariums besides water changes. For freshwater fish tanks, live aquarium plants will use up some of the nitrates. In saltwater fish tanks, live rock and deep sand beds can have anaerobic areas where denitrifying bacteria can breakdown nitrates into harmless nitrogen gas that escapes through the water surface of the aquarium.

Getting The Nitrogen Cycle Started
There are two ways to get the aquarium cycle started, either with fish or without fish.

Starting The Nitrogen Cycle With Fish
This is not the preferred way to get the nitrogen cycle started because the fish are being exposed to ammonia and nitrites during this process. Many fish can not and will not make it through the cycling process. Often times the fish become stressed and fish disease starts to break out. I wonder what percentage of disease is caused by the cycling of new aquariums?

Certain species are hardier than others and seem to tolerate the start-up cycle better than others. For freshwater tanks, the zebra danio is a very hardy fish that many use to get the nitrogen cycle started. For saltwater tanks, some have reported success using damselfish to get the process started. Again, using fish to cycle is not a good idea and you may be throwing your money (on dead fish) out the window. There is a better way. Read on, young grasshopper.

Starting The Nitrogen Cycle Fishless
There are a few different ways to get this process started. To easily get an ammonia reading from your tank water try the Seachem Ammonia Alert. It sticks inside the tank and has a circle that changes color depending on the ammonia levels in the tank.

• Option 1:
  Using Fish Food
  Drop in a few flakes every 12 hours. As the food decomposes it will release ammonia. You will have to continue to "feed" the tank throughout the process to keep it going.

• Option 2:
  Use a small piece of raw fish or a raw shrimp
  Drop a 2 inch by 1 inch chunk of raw fish or a raw shrimp into the tank. As it decomposes it will release ammonia into the tank.

• Option 3:
  Use 100% pure ammonia.
  Using a dropper, add 5 drops of ammonia per 10 gallons of aquarium water. Continue this process daily until you start to get nitrite readings with your test kit. Once you can detect nitrites you should only add 3 drops of ammonia per 10 gallons of aquarium water. Continue this process daily until you get nitrate readings with your test kit. Do a 30% water change and your tank is ready.

• Option 4:
  Use gravel and/or filter media from an established and cycled tank
  This is the best and fastest way to go. This will seed the tank with all of the necessary bacteria for the nitrogen cycle. "Feed" the tank daily with flake food until you are getting nitrate readings. Depending on how fast you were able to get the gravel and filter media into your tank, you may be getting nitrate readings in only a day or two. There are some drawbacks to this method. Ask your source if they have recently used any copper medications in the tank. If they have and you are planning to have invertebrates in the tank you should probably not use this method. Invertebrates will not tolerate copper. Get a copper test kit to determine if it's safe to use.

• Option 5:
  Using live rock in Saltwater Tanks
  The use of live rock in saltwater tanks has really taken off over the past few years. The reason for this is because it is one of the best forms of biological filtration available for saltwater tanks. The shape the rock is in when you get it will determine how long the nitrogen cycle will take. See step 7 on the saltwater setup page for more information on live rock.

• Option 6:
  Use Biospira made by Marineland. This product claims to contain some patent pending species of nitrifying bacteria that will cycle your tank in 24 hours. Some of the FishLore forum members have tried it and it sounds like it is legitimate. It is kind of expensive, but if you already have fish in your tank and they are suffering through the cycle, you may want to check this stuff out. 1 ounce of this product is supposed to treat a 30 gallon freshwater tank. There are both freshwater and saltwater versions of Bio-spira. Please let us know if you use this and if it works for you by submitting comments below.

Once the cycle has started only add one or two fish at a time. Wait a couple of weeks before adding more fish. This will give your tank the time it needs to catch up with the increased bio-load.

Speeding Up the Cycling Process
There are things you can do to speed along the process of cycling your aquarium.

• Increase the temperature of your aquarium water to 80°F-82°F (27°C-28°C)
• Get some beneficial bacteria colonies. Borrow some gravel from an established and cycled aquarium. If you have another tank with an extra filter you can use it. If you have a really nice friend with an established and cycled aquarium, ask if you can have one of their used filter media. It will be loaded with the good bacteria that we are looking for.
• There are products on the market that claim to introduce the benefical bacteria. For more information, check out this product called Cycle Water Conditioner.

  Also check out Bio-spira in option 6 above

 Buying these aquarium water test kits individually can get expensive. You can usually save a few dollars by getting a master test kit. For most hobbyists these master test kits will be sufficient. Live plant keepers and saltwater reef tank keepers may need to invest in additional specialized mini test kits such as copper, phosphate, dissolved oxygen, etc.

Some aquarium test kits come as dip strips that you dip in a test tube filled with water from your tank. You then compare the color with the card that came with the kit to get your final reading for each particular test. The other type of test kit has liquid droppers. You dispense the liquid (certain number of drops) into a test tube with tank water. You usually need to shake the tube and wait a few minutes for the test to develop. You then match the color of the water in the test tube against a test card to get your final reading. It can be a good idea to ask someone else in your house to compare the colors and give you a second opinion. Don't tell them what it means, just ask them to match up the colors. As hobbyists, we may tend to skew the results in our favor, so a second opinion may help keep us honest.

The freshwater master test kits usually contain tests for ammonia, nitrite, nitrate and pH. Saltwater master test kits usually contain tests for ammonia, nitrite, nitrate, pH and sometimes alkalinity. See below for more information on these terms.

Alkalinity
This test determines how stable your tank water is relative to a shifting pH. It can be thought of as your tank's buffering capacity or it's ability to keep the pH level stable. In most saltwater tanks you want this reading to be in the 7-12 dkH range.

Ammonia
This chemical is the result of fish waste and decomposing food in the aquarium. Ammonia is the leading killer of tropical fish. You want this reading to be 0. Read about the Nitrogen Cycle.

Calcium
Primarily for saltwater aquariums, a Calcium test kit is important to use when dosing calcium in reef tanks. Calcium is a primary element that corals need to grow and dosing calcium may be a necessity for the health of these animals. You need a test kit to determine how much and how often to dose. For more information on dosing calcium, please read Saltwater Supplements.

Chloramine
Chloramine is a combination of chlorine and ammonia. It is a stronger disinfectant than chlorine alone and is used in areas where this extra disinfectant is needed. As with chlorine, you must eliminate this chemical from your tap water before adding it to your aquarium or it too will kill your tropical fish.

Chlorine
This chemical is found in most tap water and it is used to kill the bad bacteria in our drinking water. Clorine must be eliminated before entering your aquarium or it will kill your tropical fish.

Copper
This heavy metal can come in with the tap water if you have older copper pipes. It can also get introduced to your tank if you've used any copper based medications. Copper can be very harmful to fish and invertebrates. Copper test kits

Iodine
An iodine test kit is needed for saltwater hobbists that keep corals or invertebrates that require iodine. Iodine is used up quickly by the aquarium inhabitants and skimmed with the protein skimmer.

Nitrate
Nitrites are converted to nitrates during the cycling process. Nitrates are not as toxic as ammonia or nitrites but they are harmful and will stress your fish at high enough levels. The only way to remove the nitrates is through a partial water change. Ideally you want this reading to be less than 20 ppm, in reef tanks you want this to be as close to 0 as possible. Read about the Nitrogen Cycle.

Nitrite
Ammonia gets converted to nitrite by the bacteria in your tank. Nitrite levels will soar in new tanks that have not yet been cycled. Nitrite is just as toxic to tropical fish as ammonia and the only way to quickly reduce nitrite levels is through a water change. Nitrites will eventually be converted to nitrate by the bacteria growing in the tank and filters. You want this reading to be 0. Read about the Nitrogen Cycle.

pH
pH is the scale used to measure the acidity or alkalinity of water. The scale ranges from 0 to 14 with 0 being the most acidic, 7 being neutral and 14 being the most alkaline. It is possible to raise or lower your pH levels with water changes or chemicals (use extreme caution!) from your local pet store. Different fish species require different pH levels. Try to keep fish that all require relatively similar levels of pH. Here is an article with an interesting take on pH: pH : To be or not to be considered?

Phosphate
Phosphate can be introduced to your aquarium mainly from tap water, dead plants and fish food. High phosphate levels can cause algae outbreaks. There are products on the market to remove phosphates and you can do your part by keeping up with your aquarium maintenance and performing regular water changes. Saltwater reef tank keepers and freshwater plant keepers may want to invest in a Phosphate Test Kit.

Salinity
This is the amount of dissolved salts in water and is measured using a Hydrometer.

Specific Gravity
This is a density measurement for the amount of dissolved salts in saltwater compared to freshwater. Explained another way, saltwater is composed of many more elements than freshwater. The specific gravity measurement shows us how much heavier or denser saltwater is compared to freshwater.

Water Hardness
The hardness level of water has to do with the amount of minerals that are dissolved in the water. Calcium and magnesium are the primary minerals that are dissolved in tap water. "Soft" water has relatively few dissolved minerals whereas "hard" water has many dissolved minerals. Water hardness is not really an issue unless your water is excessively soft. Then you may have problems with runaway pH levels. For saltwater aquariums this is especially true. The carbonate hardness of saltwater can give you a good indication of how stable your pH is.