Whether you’re introducing fish to a completely new tank or you’re adding a new addition to an already established tank, you’ll need to make sure that you’re doing it the right way to help protect the ecosystem, safety and happiness of your fish friends.
It’s critical to acclimatise them properly to prevent issues like pH shock, stress and, in extreme cases, the death of your tank inhabitants. In this guide, we’ll take you through everything you need to know on how to properly acclimatise your fish to new tanks, including information on all the different methods you can use, as well as the answers to commonly asked questions new fishkeepers ask themselves.
How to properly acclimate fish to a new tank
Whether it’s your first fish tank or an upgrade from your old one, there are a few different methods that you can use to acclimate your fish safely to their new environment without causing any unnecessary stress or harm. Keep reading as we share a few of the best methods that can be used for both saltwater and freshwater aquariums for getting your fish ready for their new home.
Option 1 - Acclimate your fish with the floating method
This method is known as the standard method as it’s the easiest and most widely used technique to acclimatise fish to their new environment. Before you begin this method you’ll want to use a test kit to check that the tank is suitable for your fish. We have a wide selection of test kits from pH test kits to ammonia test kits so you can be 100% sure about the quality of your water and if it’s suitable for your fish before you introduce them to their new home.
Salifert pH Profi Test Kit, £8.90 (for saltwater aquariums)
Salifert Ammonia Profi Test Kit , £10.75 (for saltwater aquariums)
NT Labs Test Kits, from £8.25 (for freshwater tanks)
To help you complete this process, we’ve laid it out in an easy step-by-step process for you, so you can be completely sure that you’re acclimating your fish to their new tank in the safest way possible.
- Gently place your fish into a clean, clear bag and ensure the bag is closed. If your fish are straight from the pet shop, you can use the bag they’ve come in.
- Ensure that the water flow in your tank isn’t too powerful to keep the bag steady and calm to avoid stressing out your fish while they acclimatise.
- Float the sealed bag in the water for 20 minutes to let the water in the bag slowly acclimatise to the temperature of your tank.
- It’s important to monitor your fish during this time for any signs of stress. This can appear in different forms such as sudden changes in your fish’s colour, and rapid breathing - which can be identified by their gills moving quickly. If they show any of these signs, remove them immediately from the tank and continue to monitor them for the next 5 minutes to ensure that these symptoms pass.
- After the 20 minutes have passed and your fish show no signs of distress, carefully open the top of the bag that contains your fish, rolling the sides down to create an air bubble so that it floats upright on the surface of the water.
- Gradually add water from your tank into the floating bag, waiting a few minutes between each addition to allow your fish time to adjust to the new water. If the bag becomes too full to add more tank water, gently pour some out into a separate receptacle.
- After repeating this process two or three times, your fish should have acclimatised and will be ready to be placed into their new aquarium. When adding your fish, make sure to use a net so that the water from inside the bag isn’t mixed with the aquarium water. Once the fish are in their new home, you can discard the bag of water.
Expert tip: We recommend turning off the lights in the aquarium during these 20-minute periods as well. This is because having a warm light next to the bag may cause the water in the bag to heat up, which could potentially harm your fish.
Option 2 - Acclimatise with the drip method
Please be aware that you can only acclimatise this way if the fish have been bought from a local shop and they have arrived at our home in less than 3-4 hours. This is because fish will take up the oxygen in the water and cause an increase in carbon dioxide and ammonia levels in the bag. If you open the bag after this long oxygen will flow in and raise the pH levels. The sudden change can cause stress to your fish as well as other illnesses and possibly death to your marine life.
The drip method is a great method for sensitive fish and invertebrates such as shrimp. To be able to carry out the drip technique you will need a few components such as:
- A clean bucket with a 12 to 20-litre capacity
- A clean airline hose
Once you’ve finally got your fish back home you can start acclimatising them through the drip method. We’ve laid this process out for you below in easy-to-follow steps
- Pour the contents of the bag into the bucket and make sure there is adequate water supply for your fish.
- Place the bucket next to the aquarium and then connect the bucket to the aquarium using your airline hose, you should tie a knot in the hose to limit water flow so that the water from the tank gradually drips into the bucket, allowing your fish to acclimate slowly to the new water. The flow rate of this hose should be about 2-3 drops per second. You can adjust the tightness of the knot in your airline hose until you achieve this.
- When you notice the bucket getting full pour out about 50% of the water out of the bucket (you should wait about 30 minutes to 1 hour) and put the tube back in and do a second round of this drip process.
- Observe your fish for any signs of distress during this process and if they are still looking healthy and relaxed you can introduce them into the aquarium.
If you’re looking for a reliable airline hose to get the job done, then we have this Kockney Koi 4mm Clear Airline that’s perfect for helping acclimatise new fish to your tank.
Kockney Koi 4mm Clear Airline for £3.59
Can you put new fish in with old fish?
The short answer is yes, you can add new fish to an established tank.
The slightly longer answer is yes, but you need to make sure to introduce your new fish in a way that limits stress on the existing inhabitants. This includes making sure that the fish you’re adding are compatible as tank mates (meaning they aren’t likely to be aggressive towards each other), and that there is enough space to support all of the fish (you can follow our ‘How many fish should you put in a fish tank?’ blog to test this), and that you follow the acclimatisation rules we’ve detailed below.
How to introduce new fish to an established tank
If you are introducing fish to an already established tank, then it’s crucial that you ensure that the type of fish you’ve chosen is suitable for the environment that you’ve created. You will need to note a few things before you add a new fish to your aquarium to keep them feeling safe and happy during this process.
- You should keep them with fish of similar origins - for example, do not mix marine and freshwater fish as they require extremely different environments for a healthy home.
- Make sure to test the water using a test kit and ensure the pH levels are the right fit for your new fish.
- Don’t add too many fish at once as this will induce stress for all inhabitants and the last thing you want is to disrupt a perfectly balanced and established ecosystem.
Frequently asked questions on adding new fish to a tank
There are many things to consider when undertaking an acclimatising process, and you might find yourself with a few questions that need answers. Keep reading as we have provided answers to some of the most commonly asked questions when it comes to acclimatising, from how many fish you can add at once to where to keep your fish during this process.
How long should I wait to add more fish to my aquarium?
You’ll need to wait for your new fish to fully acclimatise to your tank before adding any more fish into the mix. This will allow you to pick up on any issues or problems that may occur before it has the chance to affect any more fish.
We recommend that you leave it for around 2 weeks before adding a new addition to your tank. This also leaves enough time for any diseases to become apparent before any of your new fish are exposed to potential illness.
How many fish can I add at once?
When adding new fish to your tank it’s important to do it in stages, never double the amount of fish in your aquarium as this can negatively affect the ecosystem and cause potential harm to your aquatic friends. You may even find that your fish tank becomes cloudy due to the introduction of too many fish at once. If you find your tank suffering from cloudy water then you can read through our blog on how to get rid of cloudy water in a new fish tank for more tips and advice.
What happens if you introduce your fish too quickly?
Not giving your fish enough time to adjust to an aquarium can pose significant health risks to both old and new inhabitants. Below are a few of the issues that can arise due to this.
- If their previous tank had illnesses, adding that fish to a new aquarium can spread those illnesses to that tank, putting your existing tank inhabitants at risk.
- Introducing a fish to a new tank too fast can also cause issues such as pH shock from abrupt environmental changes, even to a healthy fish. Many species are sensitive to alterations in water conditions and, without the proper care, this can induce unnecessary stress in your fish, making them more prone to sickness.
How soon can you add fish to a new tank?
Tanks need to go through a nitrogen cycle first before your water can support fish. We would recommend you wait around 24 to 48 hours and sometimes up to a week to let everything from the water temperatures to lighting and pH balances settle down first. You can learn more about how to get your tank through its first cycle in our blog.
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We all want to create the best environment for our little fishy friends but if you find yourself unsure of what steps to take to create a happy and comfortable aquarium then you can browse through our full collection of beginner's guides for all the tips and advice that you’ll need for creating a thriving tank ecosystem.
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