All You Need to Know About Acclimation

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This article discusses the benefits of acclimation and the most commonly-used methods used to acclimatize fish and other inhabitants. The article then provides a detailed step-by-step set of instructions for the Drip Method, the method that is generally accepted among aquarists to be the best-practice acclimation method.

Acclimating your fish at home

In order to live successfully and happily, all living creatures need time to adequately adjust to an unfamiliar environment. Fish tank inhabitants that die within the first few days of being introduced to a new aquarium generally do so because they are not acclimatized adequately and go into shock. By following good acclimation practices you can greatly reduce the level of stress your inhabitants will endure and give them a better chance for survival. Proper acclimation should be applied to all living creatures that may be introduced to your tank including fish, invertebrates, snails, and even some plants.

This article discusses the most common methods used to acclimatise fish and other inhabitants. The article then provides a detailed step-by-step set of instructions for the Drip Method, the method that is generally accepted among aquarists to be the best-practice acclimation method.

If you wish to skip the article and go straight to the drip method instructions, click the link below.

Take me to the drip method instructions

What will happen if I don’t acclimate?
Pouring the fish along with the water into the tank as soon as you get home is fraught with danger. The best case scenario is that nothing will happen. If this is your experience, you are extremely lucky and I encourage you to go out and buy a lottery ticket. The difference between your water parameters and the water parameters from the source are a factor of the level of stress your fish will incur if they are not acclimatized properly. There is also a good chance of introducing diseases or parasites into your tank affecting your existing fish.

Before we get into the detail of the methods, it is prudent to stop for a moment and consider the importance of quarantine.

Many serious enthusiasts will consider the quarantine tank a vital piece of equipment. Quarantine tanks play an important role in reducing the risk of your new inhabitants and plants from introducing disease and parasites into the aquarium. If you have a large setup you’ve spent a small fortune on, it is no surprise to want to protect that investment by separating any new arrivals and ensuring that they are in optimum health before they are introduced to the main tank. Methods for acclimatising your fish from bag to quarantine tank and from quarantine tank to main tank are no different. You must always properly acclimatize your fish when you move them.

Is it safe to put the bag water in my aquarium?
Most people (including the author) will strongly advise against this unless under the strictest of conditions. It is simply safer to assume that the water that comes with your new inhabitants is polluted, medicated, containing parasites, or is otherwise unsafe in some way. After all, how do you know it is safe?

For a moment, assume that the bag water is free of parasites, diseases and any other countless microscopic organisms you’d prefer to avoid. The longer the fish are in the bag in transit, the more ammonia and other pollutants build up. It doesn’t take very long for the bag water to be ammonia-ridden. In addition, some fish shops and breeders add medications to water in an effort to reduce stress levels of fish during transport. Many medications are designed to kill bacteria, which is good for the fish while they’re in transit, but is no good for that vital colony of beneficial bacteria living in your filter. If the water in the water in the bag is not clear, you can safely assume some sort of additive has been used. If the bag is clear, you can’t rule out its use.

No matter which method you use to acclimatise your tank inhabitants, always dump the bag water. It’s better to be safe than sorry.

The only time you might consider transferring inhabitants from tank to tank including the water is when you are convinced beyond doubt that ALL water parameters (temperature, ammonia, nitrite, nitrate, gH, kH, salinity, etc) of the source tank and destination tank are identical and the water from the source is known to be ‘safe’. This might be the case if you have more than one tank in your home.

A note on Corals and Photosynthetic Reef Invertebrates
The need to acclimate corals and photosynthetic reef invertebrates to water is the cause of much debate amongst hobbyists. Those that advocate slower acclimation to water believe that variance in parameters between the water in the bag and the tank water may cause the coral to fall into a type of traumatized state putting the coral at risk of damaging its internal structure. Others will equalize the temperatures for around 10 minutes before putting the coral straight into the tank stating that it is counter-productive to keep it in the bag longer than necessary. Some hobbyists believe that the method and duration of acclimation should vary depending on the source or type of coral. It is not uncommon to hear of people drip acclimating corals between 30 minutes and two hours.

Regardless of which method you use to acclimate corals to water parameters, they need to acclimate to new lighting at their own pace. A good light meter is an essential tool that will go a long way in helping you achieve success in coral display and propagation. An easy way to kill your new coral is to move it around three, four or even five times during the first week to get just the right position for display purpose. Know the actual luminary requirements of your coral and secure the coral under those conditions and worry about aesthetics later.

The obvious message regarding the debate regarding acclimation of corals is to research your coral thoroughly before you acquire it. Learn its lighting and water preferences and test the parameter variance between the bag water and the destination tank. Observe your coral for evidence regarding its health status. The larger the variance in temperature, lighting and water conditions or stock that is not at optimum health equals longer acclimation time.

Before you start
Prior to picking up your new inhabitants, get your equipment out and ready to use. By the time you get home your inhabitants will be stressed from the bag-and-transit process. In order to minimize the time that they are in a state of stress, start the acclimation process immediately in order to get them out of those bags and into the tank as quickly as possible. If you are messing around looking for where you last saw that inline tubing or finding other equipment, the fish remain in the bag for longer periods and are in a state of stress for longer. It should also be pretty obvious to foresee that rushing around in a tizz when tending your aquarium equals water on floor.

Floating Bag Method
This method is probably the most popular method of acclimation and the one you will hear fish shop staff telling customers to do. The method has a few variations, but most of them involve placing the closed bag into the tank enabling it to free-float on the top of the aquarium. The bag is left for between 15 and 30 minutes so that the water temperature in the bag equalizes to the water temperature of the tank.

Once the water temperatures are the same, open the top of the bag and follow this simple 5-step process:

1. Remove 20% of the water from the bag. (If it’s fresh water, put it on your roses. They will love you!).
2. Replace this water with the same amount of water from your destination tank.
3. Wait 15 minutes.
4. Repeat steps 1-3.
5. After 1 hour, gently net the fish and transfer them to the tank.

Some fish are more difficult to net than others. If you’re having difficulty netting your fish, get a large bowl and sit the net on top. Slowly and carefully pour the bag water and fish into the net allowing the bowl to catch the water. Some people recommend performing this activity over a sink. If you choose to do this, learn from the mistakes of others and plug the drain.

This is a very popular and widely-recommended method probably due to its simplicity. One issue of concern regarding this method is the possibility of something undesirable on the outside of the bag getting into your tank. It is entirely possible that the fish shop employee used a hand-cream before handling the bags, the bags were stored on a floor, on a wet surface hence anything could have collected on them. The author specifically recalls one horrible moment when she witnessed a local fish shop owner spraying bug-killer right over the top of a pile of fish bags. Should such a bag with be floated in a tank, the consequences could be disastrous. While the risk of this occurring is considered low, it is still something to be mindful and why some will advise never to float a bag.

Important Note: Turn off your aquarium light while performing this method of acclimatisation. It will reduce fish stress levels.

The Bucket Method
This method is a variant of the floating bag method. Water from the destination tank is put into the bucket and the bag containing the fish is kept closed and allowed to free-float for between 15 and 30 minutes to allow the water temperature in the bag to equalize with the water temperature of the bucket water. The 5-step process described above then applies removing 20% of the bag water and replacing it with water from the destination tank.

The bucket method is better than the floating bag method because there is no risk of anything on the outside of the bag polluting the tank. The risk of bag water spilling into the tank is eliminated as is the possibility of anything on the outside of the bag being introduced to your tank.

The Drip Method
This method is the one used by most serious hobbyists and the one recommended above all others. The inhabitants acclimate to the new water conditions more slowly than other methods and, assuming the fish are relatively healthy when you receive them, the method ensures an extremely high success rate. The process involves using an inline tube to drip feed tank water into the bag. The water drips at a rate that both ensures temperature equality between the bag water and the tank and the difference between your water parameters and the shop’s water parameters is reduced slowly enough so that stress to the fish is dramatically reduced.

The entire process can take anywhere from an hour to two hours, depending on your own preference.

The Drip Method – Step-by-step procedure

Items Needed:

  • A fish-only bucket
  • A container or something to put your bag with fish into
  • A length of tubing/air hose (I use something around a meter in length
  • A control valve
  • A clothesline peg, airline suction cup, or similar item to secure the tube to the side of the tank

1. Discard approximately 25% of the water from the bag. Sit the bag with your new fish into a container for support. Alternatively you may want to pour the contents of the bag into the container. This can reduce the risk of smaller fish getting caught in the collapsed corner of the bag, but you may need to take appropriate caution for fish that may jump. The container should be large enough to be able to hold the same amount of water you just discarded.

Bag sitting inside container.

Notice there is enough room in this container to allow more water to be added to the bag.

2. Connect the control valve to one end of the plastic tube to create a drip hose.
Plastic tube and control valve.

3. Put the other end of the plastic tube (the end without the control valve) into the tank and secure the tube to the tank using the clothesline peg. Ensure that the end of the tube remains submerged.

4. Using a bucket to catch the water, start a siphon either by sucking on the control valve or if an additional short length of airline tubing is added to the other end of the control valve, use a children’s medicine syringe to start the siphon.
5. Adjust the control valve to let the tank water drip into the bag. Note that there is no set rate for the dripping. It can be varied depending on the sensitivity of the fish.
Starting the siphon.

Adjust the control valve to set up a drip of approximately one drip per second.

6. Place the drip hose over the bag/container allowing the water to drip into the bag.

Sometimes you may need to secure the hose to the bag or container to prevent spillage.

7. When the container has filled with water, stop the siphon by closing the control valve. Discard 25% of the water from the bag and restart the drip.

8. Repeat step 7 until the bag/container has been filled 3-4 times. The fish will then be sufficiently acclimatized to the conditions of your tank
Drip acclimation in progress.

9. Net the fish and put them into the tank. Discard the bag water.

Now that you have successfully acclimatized your fish, you can look forward to a healthy tank and happy fish. Be sure to check the water parameters several times over the week following the introduction of any new arrivals, especially if you’ve increased the bioload of the tank. Although any illnesses on the new fish should have been detected in quarantine, good acclimating procedures contribute to healthy fish and a good experience for you, the aquarist.

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