Key takeaways
- Acclimation gently adjusts new fish to your tank's temperature, salinity and pH. Rushing it is one of the most common causes of losses.
- Float the sealed bag for about 15–20 minutes to match temperature, then slowly add tank water over 30–60 minutes. Drip acclimation is the gentlest method.
- Transfer fish with a net. Never pour bag water into your aquarium.
- Keep the lights dimmed for a few hours, and don't worry if a new fish hides or skips its first meal.
New fish arrive after a stressful journey, and the water in their bag will be different from your aquarium. Temperature, salinity and pH may all have shifted during transport. Careful acclimation lets the fish adjust gradually and gives it the best possible start. At EasternMarine, every fish spends a minimum of three weeks in our quarantine systems before it's offered for sale. A good acclimation at your end completes the process.
Before your fish arrives
- Make sure your tank is fully cycled and stable. Ammonia and nitrite should read zero. Read our reef water chemistry guide.
- Check your salinity (about 35 ppt) and temperature (about 25–26 °C).
- Have the following ready: a clean bucket that has never held chemicals or soap, airline tubing with a valve or knot for dripping, a net and a thermometer.
- Plan for a quiet, dimly lit room and around an hour of your time.
Step-by-step acclimation
- Dim the lights. Turn off the aquarium lights and keep the room dim. Bright light after the dark box adds stress.
- Float the sealed bag in your tank or sump for 15–20 minutes so the water temperature equalises.
- Open the bag and transfer the fish and its water into your clean bucket. Tilt the bucket so the fish is covered.
- Add tank water slowly. Either drip tank water in through airline tubing at about 2–4 drips per second, or add a small cup of tank water every 5 minutes. Continue for 30–60 minutes until the water volume has roughly doubled or tripled.
- Check salinity in the bucket. It should now be close to your tank.
- Net the fish into the aquarium. Discard the bucket water. Never add shipping water to your tank.
- Keep the lights off for a few more hours and let the fish settle.
Acclimation methods compared
| Method | Time | Best for |
|---|---|---|
| Float and cup | 45–60 minutes | Most hardy fish |
| Drip acclimation | 45–90 minutes | Sensitive fish and all invertebrates |
| Float only | 15–20 minutes | Not recommended for marine livestock |
Shrimp, starfish and other invertebrates are more sensitive to salinity changes than fish. Use a slow drip and keep them submerged. See our reef invertebrates guide.
The first 48 hours
Normal behaviour: hiding, faded colours, fast breathing at first and not eating on day one. Most fish begin exploring and eating within a day or two.
Watch for: a fish lying on its side, gasping at the surface, white spots, torn fins or constant harassment from tankmates. If something seems wrong, test your water first, then get in touch with us.
Offer a small amount of quality food once the fish is out and about. Browse our frozen fish food and fish and coral foods.
Common acclimation mistakes
- Adding the fish straight in after floating, with no water mixing.
- Pouring shipping water into the display tank.
- Acclimating under bright lights.
- Leaving the bag sealed for hours, which lets ammonia and carbon dioxide build up.
- Adding several fish at once to a new tank, which overloads its biological filter.
Ready for your next fish?
Browse our in-stock marine fish, all quarantined for at least three weeks. Livestock is sent NZ-wide by Same Day Airfreight or overnight courier. See shipping information and our Arrive Alive Guarantee.
Products we use and recommend: Fauna Marin Salinity Reference · EMA Marine Mega Mix Fish & Coral Food · Aqua One 100W Glass Heater
Frequently asked questions
How long should I acclimate saltwater fish?
Plan for 45–60 minutes in total: about 15–20 minutes floating, then 30–60 minutes of slowly adding tank water.
Should I drip acclimate fish?
Drip acclimation is the gentlest method and is ideal for sensitive species and invertebrates. Hardy fish also do well with the float-and-cup method.
Why isn't my new fish eating?
It is normal for new fish to refuse food for the first day or so. Keep lights low, offer small amounts and check your water parameters.
