NEMO AQUA STOREHow to Cycle a New Aquarium
The #1 reason new aquarium fish die is “new tank syndrome” — adding fish to an uncycled tank. Cycling grows the invisible bacteria that convert toxic fish waste (ammonia) into harmless nitrate.
The nitrogen cycle in 30 seconds
- Fish waste and uneaten food release ammonia (highly toxic).
- Bacteria colony #1 converts ammonia → nitrite (still toxic).
- Bacteria colony #2 converts nitrite → nitrate (safe at low levels, removed by water changes and plants).
Growing both colonies takes 3–5 weeks. Until then, ammonia and nitrite spike and poison fish.
Step-by-step fishless cycle
- Set up tank, filter, heater. Fill with conditioned water and run 24×7.
- Add an ammonia source: a pinch of fish food every 2 days, or bottled ammonia.
- From week 2, test the water every few days with a liquid test kit.
- You'll see ammonia spike → fall, then nitrite spike → fall.
- When ammonia and nitrite both read 0 and nitrate is rising — you're cycled.
- Do a 50% water change, then add fish a few at a time.
After cycling
- Add fish gradually — the bacteria colony grows with the load.
- Weekly 25–30% water changes keep nitrate low.
- Never wash filter media in tap water; rinse it in tank water to protect the bacteria.
Frequently asked questions
Typically 3–5 weeks for a fishless cycle. Seeding with media from an established tank can reduce this to 1–2 weeks.
It is possible but stressful for the fish and needs near-daily water changes. A fishless cycle is safer and easier for beginners.
A water test shows 0 ammonia, 0 nitrite and some nitrate, even a day after adding an ammonia source.
Yes — plants consume ammonia directly and carry helpful bacteria on their leaves, making the cycle faster and more stable.
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