Summary: Water cycling doesn’t automatically happen just because a certain amount of time passed. A complete cycle is when tank water has stats below.

Ammonia = 0ppm

Nitrite = 0ppm

Nitrate > 0ppm (greater than 0).

What is the best environment for fish? How can we determine with observation? We will discuss that today. 

The only way to determine if a tank has been cycled is with a water test. 

It is true that a tank can be cycled after some time, but every tank has different requirements and environments, thus, a different cycle time. 

Moreover, just because a tank has been cycled, doesn’t mean that it will stay that way. It is not an exaggeration to say that any problem that arises in the tank, stems from abnormal water parameters. 

Is your fish sick? Does your tank smell? If so, you must determine if there is a problem with your water cycle. If you treat a disease or parasite without fixing the underlying problem, the water condition, the problem will never truly go away.  

That is why I believe that every fishkeeper should always have a water test kit. 

Do I have to?

API test kit can test the water’s ammonia, nitrate, nitrite and pH and can last you around 400 tests so I believe that $24 is a small price to pay. 

If you think of the time, effort and money that goes into treating your pet when it gets sick, buying a $24 test kit would require relatively less effort, stress and money. 

I believe that after one use of the water test kit, you will see why it is needed. 

When I see fishkeepers not purchasing a water test kit despite their fish getting sick and dying, it makes me sad and frustrated. Poor fish met the wrong owner and died without knowing what was wrong...

Time it takes to cycle a tank

Most people believe that it takes 1-2 weeks for a tank to cycle. In a way, that’s true. However, it means that most, NOT ALL tanks are cycled within that time.

People believe that a tank will be cycled after some time passes, however, every tank’s cycle time is different.

Parameters such as tank size and temperature are all different, and the origin and supply of the water is different as well, some coming from tap water, underground water, well water, etc.

So just because someone’s tank was cycled in 2 weeks, does not mean my tank will be cycled in 2 weeks as well.

On the other hand, it can be cycled faster. 

Therefore, it is very dangerous to assume your tank has been cycled just because a certain amount of time has passed.

Fishkeepers might think that it would be ok to put fish in an uncycled tank but the fish’s life and health is directly related to the water conditions so I do not recommend determining water cycling by time alone. 

New tank

After adding the substrate, heater and filter in your new tank, your tank would not contain any living things.

In some ways, it’s clean, or ecologically, it’s barren. 

This state is not the best environment for fish or shrimp because living things eat and excrete waste and that waste is toxic to the living things in the water.

If there are substances other than fish excrements that are rotting in the water, it is a contaminant that is poisonous to fish. 

Bacteria in the tank

A tank that living things can prosper in, is a tank with 0 ppm of ammonia and nitrite. The aquatic animals in the tank excrete waste slowly and continuously.

These excrements get broken down by the bacteria living in the tank and end up building up as nitrate.

Without bacteria, ammonia ends up building up in the tank and becoming toxic to the fish and causing disease or death. 

Why we cycle the tank

Cycling is a process we have to go through to allow bacteria to grow in the tank before adding the fish.

As stated before, contaminants in the water can occur anywhere and not just with fish excrements.

There are a lot of ways to make contaminants so please read this article for more information. 

Standard to know when cycling is completed

The only way to know when a cycle is completed is by using a water test kit.

No matter what cycling method you use, your end result must be ammonia 0ppm, nitrite 0, nitrate >0.

Relying on any other methods to determine if a cycle is complete is to rely on luck and it is unnecessarily putting your fish’s life at risk.

Based on my observation, when ammonia is in the water, the fish rubs or scratches its body on the tank surface. (This can also happen with external parasites). When you prepare food grade live fish by salting it, you can see it squirming in discomfort.

When the ammonia rises in the water, I believe it would be a similar discomfort. Based on my reading on different forums, the gills are first to become damaged. So it would be best to confirm your tank has been correctly cycled with a water test kit before placing your fish in the tank.