Dose 2 ppm ammonia. Wait 24 hours. Test ammonia + nitrite. Both 0 = cycled. Either detectable = NOT cycled.
Cycled tanks show 5-30 ppm nitrate (the end product of nitrification). No nitrate = no full nitrification yet.
Some tanks show 0/0 once but fail when retested. Run the 24-hour test 3 times across a week to confirm.
Cycling completes when pH stops dropping. A stable pH (7.6-8.2 saltwater, 6.5-7.5 freshwater) = mature bacterial colony.
Pre-stocking water change drops nitrate to safer levels (under 20 ppm). Adds replacement minerals + clears any trace medications.
Browse all cycling troubleshooting articles. Pair with the cycle ETA calculator + fishless cycle ammonia calculator.