How to Acclimate New Fish to Your Reef Tank

Why Proper Fish Acclimation Matters

When you bring home a new fish, it's been through a stressful journey. The water in the bag has different temperature, pH, salinity, and dissolved oxygen levels than your aquarium. Dumping a fish directly into your tank can cause osmotic shock, which can be fatal even if the fish initially appears fine.

Proper acclimation gives your fish time to gradually adjust to the differences, dramatically increasing survival rates and reducing stress-related diseases.

The Drip Acclimation Method (Recommended)

Drip acclimation is the gold standard for marine fish. Here's how to do it right:

What You'll Need

• A clean bucket or container (dedicated to aquarium use only)
• Airline tubing (4-6 feet)
• A way to control flow (airline valve, loose knot, or clamp)
• A net
• Timer or clock

Step-by-Step Process

1. Temperature Match (15-20 minutes)

Float the sealed bag in your aquarium or sump. This equalizes temperature without mixing any water. Don't rush this step—temperature shock is one of the fastest killers of new fish.

2. Set Up the Drip

Open the bag and pour the fish and water into your clean bucket. Position the bucket below your aquarium. Start a siphon with the airline tubing from your tank to the bucket. Tie a loose knot in the tubing (or use an airline valve) to slow the flow to 2-4 drops per second.

3. Drip for 1-2 Hours

Let the tank water slowly drip into the bucket until the water volume has at least doubled. For sensitive fish like wrasses, anthias, or wild-caught specimens, extend this to 2 hours or until the volume has tripled.

4. Net and Release

Use a net to gently transfer the fish to your aquarium. Never pour bag or bucket water into your tank—it may contain ammonia, parasites, or pathogens from the shipping process.

Alternative: Float and Release Method

For hardy fish and shorter transport times, you can use a simpler method:

1. Float the sealed bag for 15-20 minutes
2. Open the bag and add ½ cup of tank water every 5 minutes for 20-30 minutes
3. Net the fish and release into the tank

This method is faster but less thorough. Use it only for hardy species like clownfish or damsels from a trusted local source.

Special Considerations

Sensitive Species

Some fish require extra-long acclimation:

• Wrasses: Easily stressed, prone to jumping. Cover the bucket and extend drip time.
• Anthias: Sensitive to water quality changes. 2+ hour drip recommended.
• Seahorses & Pipefish: Very sensitive. Extend to 3 hours if possible.
• Wild-caught fish: May have experienced longer transport and more stress.

Lights and Activity

Keep aquarium lights dim or off when introducing new fish. This reduces stress and gives the newcomer time to find hiding spots before tank mates become too curious or aggressive.

Quarantine

Ideally, new fish should go into a quarantine tank for 4-6 weeks before joining your display. This allows you to observe for disease and treat if necessary without risking your established livestock.

Common Acclimation Mistakes

• Rushing the process: Patience saves fish lives.
• Pouring bag water into the tank: This introduces shipping waste and potential pathogens.
• Acclimating in direct light: Stressed fish + bright lights = more stress.
• Not monitoring drip rate: Too fast defeats the purpose; too slow extends stress.
• Skipping temperature matching: Even 5°F difference can shock fish.

Signs of Successful Acclimation

A well-acclimated fish will:

• Swim normally within a few hours
• Begin exploring its new environment
• Show interest in food within 24-48 hours
• Display normal coloration (though stress colors may persist for a day or two)

If your fish is gasping at the surface, lying on the bottom, or showing extreme color loss after 24 hours, something may have gone wrong. Test your water parameters and observe closely.

Final Tips

The extra time spent on proper acclimation is one of the best investments you can make in your reef keeping hobby. A stressed fish is more susceptible to ich, velvet, and bacterial infections. Give your new additions the best possible start, and they'll reward you with years of health and beauty in your tank.