Recognize the Symptoms
Fish gasping at the surface, red/inflamed gills, sudden lethargy, refusing food, glass surfing in panic.
Test ammonia immediately — if it shows above 0.25ppm, you have an emergency.
Emergency Response (First Hour)
Step 1: do a 50% water change with dechlorinated, temperature-matched water. This halves the ammonia immediately.
Step 2: dose Seachem Prime or equivalent at 5x the normal dose. It detoxifies ammonia for ~24 hours, buying your bacteria time.
- ✦Do NOT add new bacteria starter mid-emergency — focus on dilution
- ✦Keep filter running normally — do not clean or disturb media
- ✦Skip feeding for 48 hours after the emergency
Find the Cause
Common causes: filter died (check power), media replaced too aggressively, overfeeding, dead fish hidden in décor, new tank not cycled.
Test daily for 7 days after the emergency — second ammonia spikes are common.
Long-Term Prevention
Always run a backup filter (sponge filter for backup is cheap insurance).
Never replace more than 50% of biological media in one go. Stagger media swaps by 4 weeks minimum.