How to Acclimate New Corydoras in Tank?

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I understand the thrill of getting your first tank fish started. Everything is new at this point, the fish, the aquascaping activity preceding their arrival, the preparation, and the whole experience. The problem is that your excitement can turn deadly for your fish if you skip the acclimation process.

The acclimation process is necessary for all fish, including Corydoras, which we will discuss today. But why is the acclimation necessary, how long should it last, and what are the steps involved?

We’ll answer everything in today’s article, so let’s start with the beginning!

Why do You Need to Acclimate Corys?

In short – because fish need time to adapt to different water parameters. There are 2 overarching dangers to consider when it comes to moving fish from one environment to another:

  • New Tank Syndrome – This occurs when you move fish to an improperly cycled tank where nitrite levels still fluctuate dramatically. Nitrites should remain at 0 since they are as toxic as ammonia and can kill your Corydoras. If your tank cycle still hasn’t been completed by the time your corydoras arrive, consider moving them into a provisory habitat until that’s complete.
  • The stress associated with the relocation – Fish don’t like to change habitats due to all the water parameters changing along the way. All fish want is a clean environment, good food, and, most importantly, stability. A fish forced to change environments has to adapt to new temperatures, pH levels, and other water parameters as well. This transition comes with a degree of discomfort, which, in many cases, can prove fatal.

The temperature is especially concerning, given that corydoras can easily experience temperature shock due to lack of acclimation.

How Long to Acclimate Corydoras?

The entire acclimation process shouldn’t last more than an hour. This is evidence of the fish’s high adaptability, allowing it to adapt to new habitats quickly. Even so, you shouldn’t rush the process. If your fish requires double that to adapt to its new conditions, so be it.

Introducing New Cory Catfish in Tank

So, the tank is ready and fully cycled, and the fish have arrived. What next? You now need to acclimate your corydoras before setting them free into the tank. There are several reasons for that, but the main one is temperature and pH.

Your corydoras have been living in another habitat for a long time and have spent their past several hours to a day on the road in a plastic bag. Their water and the tank water will be vastly different in terms of temperature and chemical content. So, your catfish need a bit of time to adapt to their new environment.

Fortunately, you have 2 acclimation methods to consider, and we’ll break them one by one below:

Floating Bag Acclimation Method

This method is ideal if your fish have arrived in a bag, or you can move them in a bag yourself for this purpose. Make sure you keep them in the same water they came with. Then follow these steps:

  • Manage lights – Keep aquarium lights low to minimize your corys’ stress. These fish prefer to hide, and a shadier habitat will keep their stress levels low.
  • Place the bag in the tank – Immerse the bag halfway in the tank and just let it float freely. See that the bag is secure and doesn’t have any cuts or leaks, as you don’t want the bag water to seep into the tank. That’s because the fish has been sitting in it for hours, filling it with waste and harmful bacteria, none of which you want in your tank water. Set your timer to 15 minutes after placing the bag in the water and allow it to float until the timer runs off. This is enough to equalize the temperatures between the 2 mediums.
  • Cut the bag – Perform a small cut above the water level, right below the band, keeping the bag sealed. The cut shouldn’t have any contact with the tank water; I’ve already explained why. Once the 15 minutes have passed, empty approximately 50% of the bag water in a separate container (not in the tank) and then use a measuring cup to add tank water to the bag. Only add half a cup each time, making up for a small quantity of water. The goal is to acclimate the fish to their new water’s chemical content. After adding the first half a cup of water, wait for 4 minutes, and add another one. Repeat until the bag is nearly full.
  • Empty some of the bag – Once the bag is full, gently remove it from the tank, discard approximately 50% of the water down the drain, and place it back into the tank. You can now repeat the previous step and use the cup to refill the bag. Remember always to give it 4 minutes between cups to allow for a gradual transition.
  • Observe and complete – You should observe your fish’s behavior during the acclimation process. If your corydoras appear calm and remain so throughout the procedure, you can consider the acclimation step complete after the bag’s second fill-up.

Once the process is complete, transport the fish into the main tank. Caution – Always discard the bag water; only move the fish. You don’t want all that bacteria and filth to carry over to the main tank.

Dripping Acclimation Method

The dripping acclimation method is more thorough and may take up to 2 hours or more to complete. It goes without saying that most aquarists prefer the floating method because of that. This being said, the drip method also comes with some benefits, such as eliminating the risk of the fish’s water mixing with the tank water.

The steps involved in the method include:

  • Prepare the supplies – We’re talking about a 3-5-gallon bucket and a set of air tubbing necessary for the job. You then fill the bag 50% with fresh and clean aquarium water and place the fish’s bag into the bucket for temperature stabilization.
  • Fill the bag – After allowing the bag to acclimate for approximately 15 minutes, open it up and add a cup of bucket water into the bag. Wait for an additional 15 minutes, then add another cup and repeat the process until the bag is full. It shouldn’t take more than 2 cups to fill the bag.
  • Pour the bag into the bucket – You will now pour the bag’s contents, fish included, into the bucket. Do it gently so as not to splash around or disturb the fish too much. You can do this by tilting your bag to a 45-degree angle.
  • Set up the air tubbing – Get one of the air tubes and tie 2 loose knots in it. This reduces the water flow significantly since you’re looking for a dripping effect. One end goes into the tank, the other goes into the fish bucket. Place the bucket lower than the tank to allow gravity to suck in the water. Start the water flow by sucking on the tube and placing the exit end into the bucket.
  • Discard and repeat – The water should circulate at a rate of 2-4 drops per second. Supervise the process, stop the dripping, and empty 50% of the bucket water whenever the bucket fills up. Reset the entire dripping method and wait for the bucket to fill back.

After the second fill is complete, give your fish some time, around 15-20 minutes, during which you should monitor them uninterruptedly. If your fish look calm and peaceful, they’re ready for the main tank. If they feel a bit stressed, check water parameters to make sure everything’s fine on that end and give them more time if necessary.

The Best Acclimation Tips

Now that you understand how to acclimate your corydoras, you must also know the essential tips you need to prevent problems along the way. The most essential ones are as follows:

Take Your Time

Don’t rush the process! After all, the acclimation process shouldn’t take more than 2, maybe even 3 hours, depending on your acclimation method. You can’t skip the process, so you might as well do it properly for your corydoras’ sake.

Lighting Matters

Most people think of water quality and parameters when considering the acclimation process. But lighting also matters, especially for a species like Corydoras. Keep the lights low so that your catfish are calmer and more comfortable during the process.

Skip Airstones

This may sound like an unusual point until you learn that many novice aquarists use airstones to their fish bags before the acclimation begins. The idea is to provide the fish with some additional oxygenation, but the result is often completely unexpected. Airstones actually increase the water pH, causing a boost in ammonia and nitrites which can prove fatal to your fish.

Some Stress is Normal

Don’t panic if you notice your Corydoras displaying signs of stress during the acclimation process. This is normal as the fish tries to adapt to the new parameters. All should be fine so long as the acclimation process is gradual and controlled.


All fish require to undergo some form of acclimation before being added to the tank. Plus, I recommend quarantine as an additional step during the acclimation method of choice. Quarantine is necessary to monitor your fish to make sure they’re not sick or infested with any type of parasite, fungi, or bacteria.

The procedure consists of placing the fish in a quarantine tank, so you must perform an acclimation phase before that. Then you need to repeat the acclimation procedure when moving the fish from the quarantine tank into the main one.

This sounds like a drag, but it’s all worth it. After all, you’re looking to create a stable, healthy, and thriving aquatic setup which allows for no corner cuts.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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