New aquarium / filter startup & cycling

Jo Crane

Apr 23, 2009
New aquarium / filter startup & cycling

The basic explanation
The Nitrogen Cycle is the establishment of beneficial bacteria in the aquarium filter media that will help in the conversion of ammonia to nitrite and then the conversion of nitrite to nitrates.

This process can take from 2 weeks to 2 months or longer to complete.
It is vital for anyone planning on keeping aquarium fish to understand this process. Learning about this process will help you to be successful in keeping fish and it should definitely improve your chances when keeping tropical fish. The only real way to monitor the nitrogen cycle is to purchase an aquarium water test kit that will test for ammonia, nitrites, nitrates and ph.

At the beginning test your aquarium water every other day and write down your readings. You will first see ammonia levels rising. The following weeks you will see the nitrite levels rising and then ammonia levels dropping.
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 slowly don't make the mistake of loading your new tank to the max

Nitrogen Cycle Stage 1
Ammonia is introduced into the aquarium via tropical fish waste and uneaten food. The tropical fish waste and food will break down into either ionized ammonium (NH4) or un-ionized ammonia (NH3). Ammonium is not harmful to tropical fish but ammonia is.

Stage 2
Soon, bacteria called nitrosomonas will develop within the aquarium filter media 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 not more so. 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 regular partial water changes. Once your tank is established you will need to monitor your tank water for high nitrate levels and perform regular partial water changes as weekly approx 25% of your aquariums total volume.
There are other methods to control nitrates in aquariums besides water changes although live aquarium plants will use up some of the nitrates but not so that you don't have to carry out regular water changes.

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. A high 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.
Using fish to cycle is not a good idea and you may be throwing your money (on dead fish) out the window. There are better methods

Starting The Nitrogen Cycle Fishless
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 40 liters of aquarium water. If you don't get an ammonia reading with your test kit, add some more drops until you start to see an ammonia reading. Keep track of how many drops you've used so you can repeat this process daily. Continue to dose the tank with ammonia 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 40 liters of aquarium water, or if you added more drops originally to get an ammonia reading cut the amount of drops used in half. 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 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 filter media into your tank, you may be getting nitrate readings in only a day or two this is the method I prefer

Option 5:
Bacteria culture product are available to buy from LFS these will give your filter a kick start but in my opinion are no better than the used filter media method not something i have tried or tested.

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 patience are a virtue here after all you want your tank to be a pleasure for many years not a nightmare overnight :)
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