Cycling, in this case, refers to getting the tank ready for the growth of beneficial bacteria. These bacteria break down toxic ammonia and nitrite that come from fish waste, uneaten food, and decaying plants. Without these bacteria, the water becomes toxic. Fish may start gasping, turning pale, or swimming strangely. A fully cycled tank has millions of beneficial bacteria living in the filter, gravel, and decorations. These bacteria act like a natural cleaning system. Once the tank is cycled, your fish will live in stable, safe water.
2. Why Cycling Is Important
In a new setup, there are no beneficial bacteria yet, and therefore, the moment the fish start producing their excrement, ammonia builds up quickly and reaches dangerous levels.
Cycling prevents this by creating the nitrogen cycle:
Waste → produces Ammonia
Bacteria convert ammonia → Nitrite
Another type of bacteria convert nitrite → Nitrate
You remove nitrate through weekly water changes
Ammonia = deadly
Nitrite = harmful
Nitrate: safe in small amounts The goal is to let bacteria grow naturally, so ammonia and nitrite always stay at 0 ppm and nitrate stays below 20–40 ppm.
3. Things You Need Before Starting
You don’t need anything fancy, but a few basic things are important:
A filter: sponge filter or normal filter
Dechlorinator / Water conditioner
gravel or substrate
A few plants (live plants help cycling faster)
A heater (if keeping tropical fish)
Optional but helpful: water test kit
When these are ready, you can begin the process of natural cycling.
4. How to Cycle an Aquarium Naturally (Step-by-Step)
Here is a simple, safe way to cycle a tank without harming any fish.
Step 1: Set up the tank completely.
Fill the tank with water, add gravel, plants, decorations and hook up the filter. If tap water is used, a water conditioner should always be added first. Chlorine in tap water kills the bacteria you are trying to grow.
Step 2: Add a Source of Ammonia
Beneficial bacteria require ammonia to initiate their growth. To generate ammonia naturally, you can:
Drop 1–2 small fish food flakes into the tank every day
Or add a small amount of raw fish food in a mesh
It releases ammonia slowly as it breaks down.
Do not add fish yet.
Step 3: Run the Filter 24/7
Good bacteria live inside the filter. If the filter is turned off, bacteria start dying within a few hours. So never switch it off, even at night.
Step 4: Add Live Plants (Recommended)
Plants are very useful during cycling because they absorb ammonia and nitrate. Adding fast-growing plants such as Hornwort, Water Wisteria, Hygrophila, or even Floating plants will help speed up the cycle.
Step 5: Wait and Let Bacteria Grow
Cycling is not instantaneous. The bacteria need time to multiply. Typically it takes:
2–4 weeks for small tanks
4–6 weeks for larger tanks
Avoid full water changes during this period. Only top up evaporated water and remove extra waste, if necessary.
Step 6: Test the Water (or Follow Signs)
If you have a test kit:
First, ammonia will rise
After a few days, nitrite will rise
Nitrate will appear after 2–4 weeks.
When ammonia = 0 and nitrite = 0, your tank is cycled.
If you don’t have a kit, you can look for natural signs:
Water becomes cloudy then clears
Plants start to grow better.
A light brown layer (beneficial bacteria) forms on filter sponge
Tank smell becomes earthy, not foul
These are indications of bacterial growth.
5. When Is the Tank Fully Cycled?
Your aquarium is considered cycled when:
Ammonia stays at 0 ppm
Nitrite stays at 0 ppm
Nitrate is present but less than 20–40 ppm
Only then is it safe to add fish.
6. Adding Fish the Right Way
When your cycle is complete, add fish in small steps, not all at once. Add 2–3 fish and wait one week, then add more. Give the bacteria time to adjust to the new waste level.
Never wash the filter sponge with tap water; use tank water so bacteria don’t die.
7. Mistakes to Avoid While Cycling
These mistakes are frequently made by beginners:
Adding fish on day one
Doing full water changes
Washing filter with tap water
Die Filterung aussetzen
Adding an excess of food as ammonia source
Using strong chemicals
Not using a water conditioner
Avoiding these mistakes makes the cycling smooth and safe.
8. How to Make Cycling Faster (Natural Ways)
You can accelerate the process naturally by:
Adding water from an established tank
Using old filter media from another aquarium
Adding more live plants
Maintaining a stable temperature
These methods introduce bacteria faster and reduce cycling time.
Conclusion
Cycling an aquarium is the foundation of healthy fish keeping. When you understand the cycle and give it time to develop naturally, your fish live longer, stay active, and rarely get sick. It may take a few weeks, but it saves you from losing fish later. A properly cycled tank becomes its own balanced world, where good bacteria, plants, and fish work together in harmony. For any beginner, learning this process is the first step towards becoming a successful aquarist.