Aquarium Cycling

Aquarium cycling actually refers to the nitrogen cycle. It is a process where waste products from your fish converts from harmful chemicals to harmless chemicals, naturally!



Getting Started Cycling Tank.

The following describes the chemistry changes that occus in your new aquarium before it balances naturally.

During cycling, the fish inside will be stressed because and they may die or fall sick before the balance is reached. To cycle the tank, you should use cheap and hardy fish because they are tough enough to handle this difficult mission!

Ok I know you're on the starting line all ready to go so lets get started!

What you need:


  • A fish tank (of course)
  • cheap, hardy fish
  • A Biological Filter setup (The term setup is used because a bio filter is not complete without established bacteria colonies. Aquarium cycling is all about establishing these bacteria. If you need help on a bio filter setup, you can refer to the aquarium filtration section.



Day 1

There are people who top up the tank with water and leave it for a week or two before putting the fish. Skip those wasted time! Let your tank stand for 1-2 days is more than enough! The tank does not start the cycling process without ammonia, and that comes only from fish waste! Just remember to add a correct dose of antichlorine+antichloramine to the water you use so as to remove chloramine and chloramine. Chlorine and chloramine are added by the water supply company to kill bacterias to make it safe for humans to drink. However, when we do aquarium cycling, we need bacterias to multiply to eat the fish waste, so help the bacterias! They are our friend.

Note: Bacterias that help in the cycling process are grouped together and called 'beneficial bacteria'. We want to preserve them and let them multiply in our filtration systems!

To add ammonia to the water, cheap hardy fish should be introduced. Anywhere from two to five inches of fish may be used per ten gallons of water (any less and the tank may go through another, but smaller, cycle when more fish are added in future; any more and the water condition may go beyond what your hardy fish can tolerate). Ammonia is produced from fish waste. In short, your fish eats food and converts it to ammonia.

In the first day, with the introduction of the cheap, hardy fish, there should not be enough ammonia produced to be measured because it is diluted by the volume of nice clean water. Therefore,

All readings should be near zero.



Day 2

Feed the fish as usual, but not too much until there is leftovers in the tank. Leftovers rot and can cause the waste levels to go out of control. Don't forget we are not changing water throughout the cycling process! (Did I hear 'yay!' ?).

Remember that during cycling, we try not to change the water because we don't want to prolong the time it takes for the tank to cycle. Everytime you chance water, you are removing the waste chemicals that we need!.

Important!: Used aged water or dechlorinated water only! The smallest amount of chlorine will set you back in the cycle, especially in the beginning stages where beneficial bacteria is still in minute quantities.

If changing water is absolutely necessary, keep it small and less than 20% of the total water volume. Best if you don't change at all.

Ammonia should be rising to a measurable amount.



Day 3

Ammonia rises quickly to almost dangerous levels. You should see a spike in the ammonia level if you are actively testing the water. The fish in the tank should show signs of stress due to the water condition going bad.

During this period, be careful not to feed too much because the fish may lose their appetite. Put a little food at a time and only put more if the food is finished.

Also, control the amount the fish eats. You should not always feed until the fish won't eat anymore. It is generally better to keep the fish a little hungry. Especially when feeding dry pellet foods, a fish may become overfull when the food absorbs water and expands in the stomach. It is better to feed a more small meals than less big meals.

First stage bacteria are consumming ammonia and converting them into nitrite. However, as the bacteria is still very little, only a very small amount of ammonia is being converted into nitrite. As the ammonia being consumed by bacteria is less than the ammonia the fish is producing, ammonia levels in the tank continues to rise, however, at a slower rate.

First stage bacteria are growing to become established, but the amount is still very low.

Nitrite level in low, unmeasurable quantity.



Day 5

Ammonia level maxs out and starts dropping. This is because the first stage bacteria has grown in quantity to be able to consume ammonia and converts them to nitrite faster than the fish can produce them. The result is a drop in ammonia level and rise in nitrite level. During this time of maximum ammonia, less hardy fish may fall sick or even die.

If you observe your fish having difficultly coping, you may want to change some water in the tank so the ammonia is more diluted. As warned earlier, use aged and dechlorinated water only! Don't change the water if not absolutely necessary.

Ammonia maxs and drops.

Nitrite levels rising.



Day 8

First stage bacteria are now well established. Ammonia level drops at a faster and faster rate and finally to zero. Nitrite levels begin to rise faster than before. During this time when the ammonia drops rapidly to zero, you will notice the fish becoming active and happy, looking for food, fighting, getting active. This is because this is their first break from the stressful "work" in the last few days. Congrats, you are halfway there already!

First stage bacteria well established.

Temporary improvement of water condition.



Day 14

Nitrite levels has climbed to reach the maximum levels. Again, fish in the tank will start to show stress. During this time, partial water changes can be made but I don't need to tell you now, change less than 20% and use de-chlorinated water only.

Nitrite levels maxs.



Day 27

During the last few days, second stage bacteria grows as they consume the nitrite and converts nitrite into nitrate. Nitrite levels continue to be elevated for several weeks.

Nitrite being converted to nitrate by second stage bacteria.



Day 29

Second stage bacteria are well established. These second stage bacteria are able to convert nitrite as fast as they are produced. Nitrate levels now becomes measurable.

Second stage bacteria well established.

Nitrate levels rises.

Day 30

Both first and second stage bacteria are now well established. Ammonia produced by fish is converted into nitrite and then nitrate with no excess because there are now enough fisrt and second stage bacteria to process them. Congratulations! Your tank is fully cycled and ready for your fish to be put in!

Tank is cycled !



additional notes:

1. A rise in nitrate levels after the tank has cycled may cause an algae bloom. This is because nitrate is a plant nutrient. To prevent excess algae, you may want to put in some water plants to absorb and use the nitrates as they are produced by second stage bacteria. This effectively starves the algae of the nutrients they require, bringing them under control. Also, you will have happy plants!

2. Although the tank has fully cycled, it is important to continue to look after the beneficial bacterias in your tank through proper maintainance practices. Read about maintaining your biological filtration here.


If you want to use do a cycle without fish, then this fishless cycle article may be useful.


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