What Happens If You Don’t Acclimate Aquarium Fish?

What Happens If You Don’t Acclimate Aquarium Fish?

When you’ve just arrived home with a new fish for your aquarium, the first thing you’re tempted to do upon coming in the front door is dumping them directly into their new home. However, it’s important to acclimate your new inhabitant first — but why?

What happens if you don’t acclimate your fish before adding them to your tank?

What Is Acclimating?

Acclimating is, put simply, the act of adapting to new surroundings or situations. When it comes to fish keeping, acclimation is the process through which a new fish adapts to the parameters of its soon-to-be new home. 

A new fish must adapt to different water parameters, different/new tank mates, different decor/setup, and much more. The acclimation process, when done correctly, gives the fish some time to get used to these changes before being thrust into the midst of them, which can cause stress. 

What Happens If You Don’t Acclimate New Fish?

If you fail to acclimate your fish before you add them to your aquarium, you run the risk of your fish suffering from a variety of illnesses, troubles, and misfortunes. 

Most commonly, fish that aren’t properly acclimated will suffer from increased and prolonged levels of stress. For fish, stress can be deadly — especially when it lasts for a long period of time. Unfortunately, when a fish is dumped into new surroundings without being given time to adjust, the body becomes stressed and stays that way as it struggles to adapt. 

An increased stress level can leave the fish in question more susceptible to illnesses including fungal infections and problems with their swim bladders (the organ that helps a fish maintain its ability to float and stay upright). 

Fish can also suffer from shock when they’re not acclimated. You can think of this shock as being similar to the shock you experience when you jump into a cold pool, except that the fish can’t just get out and are forced to continue to endure the shock. 

In some cases, lack of acclimation can lead to death. This can happen as a result of stress or shock, or because the new environment isn’t suitable or adequate for the fish being introduced. Typically, death due to poor acclimation happens within a matter of days. 

How To Acclimate Fish: Two Methods 

There are two methods that are used to acclimate new fish. Both are relatively simple and can be done by anyone, regardless of their experience within the aquarium hobby. There are 6 easy steps for each method and we’ve outlined them below. 

Drip Acclimation 

  1. Whether you purchase your fish online and have it shipped to your door or whether you’ve picked it up at a local pet store or breeder, you’re going to receive it in a sealed plastic bag. Take the entire plastic bag and set it in your aquarium, allowing it to float on top of the water for 20 to 30 minutes. This part of the process is known as “temperature acclimation”, during which the fish will adjust to the temperature of the water of your aquarium while still being safeguarded by the temperature of the water in their shipping bag. 
  2. Fill a 5-gallon bucket with aquarium water so that it’s roughly halfway full. You can do this anyway you see fit, but most people just use a clean container to transfer water between the two areas. 
  3. Remove the bag from your aquarium and carefully open it. Dump the water and your fish gently into the bucket. Be sure that there is enough water in the bucket to fully submerge the fish before doing so.
  4. Use an aquarium siphon to siphon water from your aquarium into the bucket. You want to finish filling up your bucket. By using the siphon and controlling the flow of water into the bucket, the temperature and PH of the water within the bucket changes more slowly and gradually, which is beneficial to your fish,

If you find that the water is siphoning too quickly, you can tie knots in your siphoning tube to slow down the flow. 

  1. Discard half of the water in your bucket and repeat step 4. 
  2. Use a cup or bag and scoop the fish out of the bucket, gently releasing it into the aquarium. 

Floating Acclimation 

  1. Start by switching off the lights in your aquarium in preparation for your new addition. Bright lights can cause undue stress in your new fish, so switching them off is always a good first step.
  2. Proceed to temperature acclimate your fish by floating them, in a bag, in your aquarium. Allow your fish to sit like this for 30 minutes or so.
  3. After the bag has floated for a period of time, open the bag and carefully roll down the edge so that an air pocket is created. Be sure not to simply cut the bag open, but instead take your time to undo the elastic or plastic clip that was holding the bag closed.
  4. Slowly start to introduce aquarium water into the bag. Start by adding half a cup of water and add another half cup every 5 or 6 minutes until the bag is full. 
  5. Discard half of the water in your bag and repeat step 4. 
  6. Using your hands or a net, remove the fish from the bag and introduce them into the aquarium. Try your best not to let any of the bag water get into the aquarium. 


If you don’t acclimate your fish before adding them to your existing aquarium, you could end up with a variety of problems on your hands. From fish who are stressed out and develop illnesses, to fish who end up dead within a matter of days, there are a number of unfortunate events that can take place when this important step is skipped, forgotten, or rushed. 

You can acclimate your fish using either the drip method or the floating method, both of which are gentle and require minimal preparation or equipment. 

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