Dose Seachem Prime which detoxifies ammonia for 24-48 hours. Verify temperature + pH. Identify if ammonia or nitrite spiked.
Drop ammonia + nitrite via dilution. Match temperature + pH of replacement water. Use Prime in new water.
For the next 2 weeks: 25% daily water change with Prime. Test daily. Bacteria will catch up; fish survive if you can keep parameters detoxified.
Less food = less waste = less ammonia. Fish can survive a week without food in the cycling phase.
Dose Bio-Spira or Stability daily for 7-14 days. Speeds bacterial colonization to take pressure off fish.
Fishless cycling with pure ammonia + bottled bacteria is humane + faster + cheaper. Don't repeat this mistake.
Browse all cycling troubleshooting articles. Pair with the cycle ETA calculator + fishless cycle ammonia calculator.