1.1 Acclimation Guide for Marine Fish

Acclimation Guide for Marine Fish

  1. Important: Set up the aeration first. Have a heavy air stone and strong enough air pump.
  2. Attach the air stone to pump through airline tube, turn on the air pump, and drop the air stone into a large enough acclimation container (like a 5-gallon bucket). This is the most important step. You may end up killing fish if you don’t run aeration while acclimating the fish
  3. Empty out the fish bags into the acclimation bucket. Make sure all fish going in the bucket are compatible with one another. For example, we don’t want to put an angler or a lionfish and a Green Chromis in the same bucket, then chromis will be most likely swallowed by the lionfish. If you have incompatible species, then you may need more than one acclimation set up or you may have to acclimate in two batches.
  4. Syphon the water from your main tank (where the fish are going to go in) and let the water flow in your acclimation bucket without restricting the flow. Do not tie a knot or restrict the flow in any form. We don’t want drip acclimation, but we want full flow acclimation. Keep an eye on aeration and make sure enough air is fractioned. We do not recommend drip acclimation for our fish shipments, but we recommend Flow Acclimation.
  5. Let’s say your acclimation bucket has one gallon of water to start with (from emptying the fish bags into it), Then you need to wait till the total volume becomes at least three gallons by the flow via airline tube. Once again, please do not restrict the flow in any form. We want unrestricted free full flow of water through the air line tube. When the water volume has tripled approximately, you may remove half of the water (about 1.5 gallons) from the acclimation bucket and discard the water. Wait till the water volume becomes three gallons again.
  6. Now your fish is ready to be placed in the main tank. Catch the fish and put it into your main tank.
  7. The whole process should not take more than 10 to 15 minutes. Fish are breathing specimens and one of the major reasons for fish death during acclimation is oxygen depletion during the acclimation process.
  8. Important: Please do not use heater in acclimation bucket as temperature and dissolved oxygen concentration in water have an inverse relationship. In summary, if you put heater in acclimation bucket then the water’s oxygen level will be depleted very quickly killing your fish. Keep in mind that the oxygen levels in the shipping water will be already somewhat low because of fish breathing during the shipping time period, and do you want to turn on the heater and bring the oxygen level close to zero? DO NOT USE HEATER in acclimation bucket during acclimation process.


  1. Why is acclimation needed for marine fish?

The water parameters of your main tank may be different from that of the water in the shipping bags. For example, the temperature, pH, and other parameters of the main tank water will be somewhat different from that shipping bag water. Fish need to go from shipping water parameters to your main tank water parameters and this process cannot be sudden or abrupt. Fish need to get used to the main tank water parameters slowly so that the fish is not shocked. Keep in mind that too long of an acclimation is also not good for fish as temperature gradience will set in, and oxygen may be depleted etc. Too long of an acclimation may hurt your fish (more than 40 minutes), so we recommend our quick Flow Acclimation which should only take about 10 to 15 minutes. 

  1. What type of acclimation is needed?

We Strongly recommend Flow Acclimation, and we do not recommend drip acclimation for fish shipped from us. For our shipping method we recommend only Flow Acclimation.

  1. Can I acclimate fish, corals and invertebrates together?

It is not a good practice to acclimate fish, corals and invertebrates together. Let’s say the supplier ships fish with some level of copper, other unknown medications that could kill corals and invertebrates or let’s say the supplier ships with hypo salinity water (we don’t ship like that, but we just want to give you some assumptive situations). Also keep in mind that fish needs different types of acclimations from corals and invertebrates, it is always good to separate fish from corals and invertebrates.

  1. Can I acclimate corals and invertebrates together?

Usually yes, however there are some exceptions. We don’t recommend acclimating shrimp or starfish along with corals. Shrimps and Starfish are so sensitive that you need to set up a separate acclimation bucket for them and need to drip acclimate them for at least 45 minutes (should not Flow Acclimate Starfish or Shrimps)

  1. Does this method apply to all of the marine fish?

There are some exceptions where Flow Acclimation may not apply. The Sharks and Rays are very sensitive to pH change. When fish is shipped the fish may poop inside or there may be other forms of excretion that may release ammonia which in turn will lower the pH of the water even close to 5 sometimes. Let’s say if the shipping bag has plenty of water, then this sort of pH getting low during the shipping duration is somewhat minimal; however, if the fish were packed with low amount of water, then the pH of the water will be significantly lower. Sensitive Fish like sharks and Rays will die if the acclimation is very fast as they can’t withstand this sort of pH shock. For sharks and Rays, it’s still better to do flow acclimation when shipped from us. We add plenty of water and oxygen to shipping bags and the pH doesn’t go too low during our shipping method. But if you receive sharks or Rays from some other supplier with very less water in the shipping bag, then you may consider doing a drip acclimation or you can follow whatever method that supplier had recommended you.

  1. Can I put heater inside the acclimation container when acclimating?

Heater should never be used inside the acclimation bucket as water temperature has inverse relation with the amount of oxygen dissolved in the water. Oxygen concentration is inversely proportional to water temperature. Fish bags already will have depleted levels of oxygen as the fish had been breathing inside the bag for several hours during shipping, and when you put a heater inside the acclimation bucket and remove even more oxygen from the water the fish will certainly die.

Also, fish can get burns when they touch the heater tube, so we don’t recommend heaters inside the acclimation bucket.

  1. Can I bubble air with a tube alone without the air stone?

No, this doesn’t help much. Air needs to be fractioned into small bubbles for the oxygen from the air to diffuse into water. For a given volume, smaller bubbles have more surface area than a single large air bubble, and more surface area means more diffusion of oxygen from the air to water. So, use heavy air stone that sinks in the water. Do not use a light air stone that floats on the water as it will not get the job done in getting that oxygen into water.

  1. Is longer acclimation usually better than shorter acclimation?

No, we always recommend short acclimation for our fish. Fish are heavily breathing organisms and the longer they are in the acclimation bucket, the more chance for them suffer from oxygen depletion. A quick 10 to 15 minutes acclimation with unrestricted flow does the acclimation job very good in our opinion. A long acclimation of 40 minutes or more had resulted in negative ways for us and for that reason we always recommend quick simple Flow Acclimation.

  1. What are the Pros and cons of acclimating fish?


  • minimizes the shock that the fish goes through
  • minimizes long term organ damage to fish
  • fish may start eating soon after acclimation when done correctly and may adjust to aquarium conditions very fast within hours after they had arrived.


  • It’s needed. Acclimation is necessary and you shouldn’t skip acclimation
  • So many hobbyists kill a lot of fish by drip acclimation which may go wrong when done incorrectly resulting in oxygen depletion. If you saw the fish swimming and alive in shipping bag; yet, died after acclimation, then it is most likely that the acclimation set up wasn’t incorrect, or the acclimation process was done incorrectly.
  • It is very easy to set up the acclimation incorrectly and kill fish.
  • Often confusing as different suppliers may recommend different acclimation methods.
  1. Can I float the bags in my main tank for 10 minutes before emptying out in the acclimation bucket so that the bag water temperature is same as main tank. In other words, can I temperature acclimate by floating the fish bags in my main tank?

You do not need to float the bags in your main tank for the Flow Acclimation that we recommend. During the flow acclimation, the flow is so high that the temperature of the water in the acclimation bucket will get very close to the main tank water very quickly. Time is of the essence here, as the fish have traveled a long distance inside a bag, and the water inside is already polluted. We don’t want to keep them inside the shipping water anymore time than what is really needed. So, save those 10 to 20 minutes float time, skip it and get to the process of Flow Acclimation right away.


Notes and Disclaimer: Our recommendation for Flow Acclimation is based on our empirical knowledge. Our goal is not to argue or disagree with hobbyist’s or other suppliers’ opinions or recommendations, but to give some really helpful advice which we acquired through several years of experience in handling live marine fish. If you ask for a peer reviewed paper, then I don’t have one, and if you need a peer reviewed article to be conviced to use our method, then please follow your own acclimation method. This document is published so that it can help hobbyists successfully acclimate their fish, and there is no compulsion for the anyone to follow our method. We are not responsible for any claims of fish loss or any livestock loss because of you following our procedure. This document is purely for information purpose only.