How To Acclimate Fish

It is absolutely essential that you acclimate fish before introducing them to your tank. Properly acclimating your new arrival could mean the difference between a healthy, happy fish that has found a new home, or one that is doomed to perish after several hours in your tank.

Why Do We Have To Acclimate Fish?

Put simply, we have to acclimate fish because the water parameters in the shipping bag and the water parameters in our tank are usually very different.

Primarily, we have to acclimate fish to differences in pH and temperature, so that they can make a smooth transition from the shipping bag to our tank.

If the fish has spent an hour or so in the shipping bag in the journey from the LFS to your home, the pH of the water would have gradually dropped. Marine fish drink copious amounts of water from their surroundings and excrete highly concentrated urine. This increases the acidity of the water in the shipping bag, lowering the pH considerably.

If a fish is introduced suddenly to water with a higher pH or lower pH without proper acclimation, osmotic shock results.

Osmotic shock, depending on the severity, can lead to a stunned, weakened fish. In some of the more delicate species, it may even result in death after a few hours.

How To Acclimate Fish

The procedure used to acclimate fish is very simple and takes about 45 minutes to an hour. What we are doing is that we are slowly introducing water from our tank and gradually allowing it to mix with the water in the shipping bag that the fish is in.

Once enough time has passed and  we have at least doubled amount the amount of water in the shipping bag, the fish can be released into the tank.

How To Acclimate Fish | Basic Procedure

Once you open the top of the shipping bag, place the entire bag in a plastic container narrow enough to keep it standing upright. Ensure that the bag cannot collapse on itself and that the fish is not caught in one of the corners of the bag as it sits in the container.

With a water jug, scoop out water from the tank that the fish will be placed in. I hope, in your case, that it is a quarantine tank for your newly arrived fish.

Carefully dribble about 30mls of tank water into the shipping bag. Slowly pour the water in along the side wall of the bag so the fish is not startled. Wait for 10 minutes before slowly pouring in another 30mls of tank water.

Pour in 30mls of tank water at 10 minute intervals until the amount of water in the shipping bag has at least doubled. Be patient and take however much time that requires.

Some LFS’s will put too much water in the shipping bag, in which case you will have to discard a third or even half of the water first, before you begin acclimation. As long as the fish is comfortably submerged, with at least 3 inches of water above its dorsal fin, it will be fine and you can start the acclimation procedure.

For bigger fish in a larger volume of shipping water, you can increase the amount of water you pour in each time, but keep the 10 minute interval the same.

After the hour has elapsed and the volume of water in the shipping bag has at least doubled, gently pour the water and the fish into a perforated plastic colander and release the fish into the quarantine tank. We want to discard all of the shipping water that the fish was in.

Most aquarists use a net to remove the fish from the shipping water. Nets can snag fins, mouths and gills which is why I prefer a colander or strainer. Make sure that the colander has no sharp edges in its perforations that might hurt the fish and dedicate a new one only for this purpose. It is probably not a good idea to use the same strainer for salads or that family pasta.

Even if your dealer’s tanks appear healthy and free of disease such as ich or white-spot, we should never risk the health of the inhabitants in our main tank. Quarantine all new livestock!

How To Acclimate Fish | Drip Acclimation

The best and most gradual way to acclimate fish is by drip acclimation.

With drip acclimation, water from the destination tank is siphoned and dripped via airline tubing into the shipping bag. The rate of the drip is controlled by a simple plastic valve that should be adjusted to, say, one or two drops of water per second.

Drip acclimation ensures that the water form the destination tank enters the shipping bag at a very gradual rate and the fish is allowed to slowly acclimate. With drip acclimation I prefer to let the process carry on for a full hour, or 90 minutes even.

Care should be taken that the drip valve is doing its job. We do not want a sudden siphon of water filling the bag which would defeat the purpose of gradual acclimation!

After the drip acclimation procedure, the shipping water should be discarded completely and never reused! Remove the fish as described above and place it in the quarantine tank.

Always Acclimate Fish Properly!

Some LFS’s tell the beginner that all they need to do to acclimate fish is to simply float the shipping bag in the tank before releasing the fish. This is inadequate acclimation procedure!

While this ‘method’ equalizes the temperature of the water in the bag to the water in the tank, this does NOT count as proper marine fish acclimation since the all important issue of pH difference and osmotic shock are not addressed by simply floating the bag.

Floating the bag is useful only as a pre-acclimation procedure, especially if the temperature difference between the water in the shipping bag and the water in your tank are several degrees apart.

Read more about Aquarium Livestock:

Quarantine Tank

Mandarin Fish | Care and Feeding

Feeding Marine Fish

Aggressive Fish

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