Step-by-step
Step 1: Quarantine the new fish first21-30 days saltwater (with prophylactic copper) or 14-21 days freshwater (observation only) in a separate QT tank. Mandatory for marine; highly recommended for freshwater.
Step 2: Drip acclimate to display parameters60-90 minute drip acclimation. Match salinity + temperature within 1°F + 0.001 SG.
Step 3: Plan introduction at lights-offAdd at the END of the lights-off cycle (or with lights off entirely). Resident fish are calmer + less territorial in the dark. New fish acclimates without immediate stress.
Step 4: Rearrange the rockwork (optional)For semi-aggressive species: move the rockwork before adding the new fish. Disrupts existing territories so the new fish has equal claim.
Step 5: Net into the displayNever pour shipping water. Use a fine-mesh net.
Step 6: Lights low for 24 hoursKeep lights at 30% or off for first 24 hours. Don't feed for 24 hours so the new fish acclimates without digestive stress.
Step 7: Observe for 7 daysWatch for aggression - chasing, fin nipping, hiding. If sustained, separate the aggressor and try again with rockwork rearranged.
Step 8: Hold off on additions for 30 daysAfter successful introduction, wait 30 days before adding more fish. Stable bio-load + parameters.
Frequently asked questions
How do I introduce a new fish without aggression?
Add at lights-off, rearrange rockwork to disrupt territories, add multiple peaceful fish at once if needed (dilutes aggression).
Can I skip quarantine for fish from a trusted source?
Marine: never. Even reputable vendors miss carrier-state ich/velvet. Freshwater: lower risk but still recommended.
How many fish can I add at once?
Marine: 1-2 max per addition. Freshwater community: 4-6 (small school species). Always within bio-filter capacity - avoid more than 25% increase in bio-load per addition.