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When can I add fish?

Q: How long does it take to cycle a fish tank?

A fishless cycle usually takes 4 to 6 weeks; a fish-in cycle 5 to 9 weeks. Warm water (about 80°F) and bottled bacteria can speed it up.

Q: How do I know the cycle is finished?

Your test kit reads 0 ammonia and 0 nitrite, with some nitrate, on two days in a row, 24 hours after dosing 2 ppm ammonia (fishless) or after a normal feeding (fish-in).

How long does it take to cycle a fish tank?

Fishless usually takes 4–6 weeks; fish-in 5–9 weeks. Warm water (about 80°F) and bottled bacteria can speed it up.

How do I know the cycle is finished?

0 ammonia and 0 nitrite, with some nitrate, two days in a row, 24 hours after dosing 2 ppm ammonia (fishless) or after a normal feeding (fish-in).

What is the cycle, anyway?

Bacteria in the filter turn toxic ammonia into nitrite, then into much safer nitrate. The nitrogen cycle, explained.