How to cycle a tank (understanding the nitrogen cycle)

The Key to a Safe, Healthy Aquarium

Cycling a tank means growing beneficial bacteria that convert toxic fish waste into less harmful compounds. This is essential for any healthy aquarium.

What is the Nitrogen Cycle?

Ammonia (NH₃): Comes from fish waste, decaying food

Nitrite (NO₂): Formed as ammonia breaks down — also toxic

Nitrate (NO₃): Final product — less toxic, removed with water changes

The Cycle Process:

1. Ammonia spike — from waste or ammonia dosing

2. Nitrite spike — as bacteria begin converting ammonia

3. Nitrate appears — final stage; ammonia and nitrite drop to zero

4. Tank is cycled once ammonia & nitrite = 0, nitrates 5–40 ppm

How to Cycle a Tank:

Option A: Fishless Cycling

Add bottled ammonia or fish food to simulate waste

Use bottled bacteria (like Seachem Stability)

Monitor water daily

Cycle time: 2–6 weeks

Option B: Fish-In Cycling

Add hardy fish like snails or minnows

Use water conditioner (e.g., Prime) daily to neutralize ammonia

Feed lightly

Cycle time: 4–8 weeks with close monitoring

Test Water Regularly:

Ammonia, Nitrite, and Nitrate using a liquid test kit

Do partial water changes if ammonia or nitrite > 1 ppm

When Is It Fully Cycled?

Ammonia = 0

Nitrite = 0

Nitrate = 5–40 ppm

Can now safely add fish

Tips:

Don’t clean filters during cycling

Add live plants to speed up the process

Patience is key — rushing leads to fish loss