How to Cycle Your Aquarium

What Is the Nitrogen Cycle?

Every aquarium is a living ecosystem. When fish eat, they produce waste that breaks down into ammonia, which is highly toxic. Beneficial bacteria convert ammonia into nitrite, then a second colony converts nitrite into the far less harmful nitrate. This biological process is the foundation of a healthy aquarium.

Without a cycled tank, ammonia and nitrite spike as soon as fish are added, leading to stress, illness, and death. Cycling your tank before adding fish is the single most important step in fish keeping.

Fishless Cycling (Recommended)

Fishless cycling involves adding an ammonia source to an empty tank and letting bacteria colonize over 4 to 6 weeks without putting any fish at risk.

Step 1: Set Up Your Tank

Fill with dechlorinated water, install your filter and heater set to 25-28°C. The filter is where most beneficial bacteria live.

Step 2: Add an Ammonia Source

• Dr. Tim's Ammonium Chloride: The cleanest option — add drops to reach 2-4 ppm ammonia.
• Fish food: Drop a pinch of flake food and let it decompose.
• Raw shrimp: Place a piece in the tank — it will rot and produce ammonia.

Step 3: Test Daily

Use a liquid test kit like the API Freshwater Master Test Kit (test strips are less accurate):

• Week 1-2: Ammonia rises, nitrite stays at 0.
• Week 2-4: Ammonia starts dropping, nitrite spikes.
• Week 4-6: Nitrite drops, nitrate appears.

Step 4: Confirm Completion

Your tank is cycled when you can add 2 ppm ammonia and it converts to nitrate within 24 hours, with ammonia and nitrite both reading 0 ppm.

Step 5: Add Fish

Do a large 50-70% water change to bring nitrates below 20 ppm, then add fish gradually — not all at once.

Pro Tip: Seed new filter media by squeezing old filter gunk into the new tank — this transfers bacteria and cuts cycling time to 1-2 weeks.

Common Mistakes

• Adding fish too soon: Wait until the cycle is 100% complete.
• Cleaning the filter during cycling: Never rinse media in tap water — chlorine kills bacteria.
• Stopping ammonia dosing too early: Keep dosing until the cycle is confirmed complete.

Signs Your Tank Is NOT Cycled

• Ammonia above 0 ppm
• Nitrite above 0 ppm
• Fish gasping at the surface
• Unexpected fish deaths

Cycling with Live Plants

Live plants can help by absorbing ammonia directly. Fast-growing plants like hornwort, elodea, and floating plants are especially effective during cycling.