How long should you wait before putting fish in a new tank?

Quick Answer: It takes 2 to 6 weeks to cycle a new aquarium to establish beneficial bacteria. After that, add fish gradually, starting with hardy, small fish to avoid overloading the tank with waste.

Why? well.

Imagine a stranger abruptly taking you from your home and your family/friends.

That’s bad enough.

Now imagine you’re taken to a mysterious location and dropped off to start your new life with no time to process what’s happening.

Needless to say, this would be more than a tiny bit stressful for anyone, and it’s no different for a fish.

When starting an aquarium, the first thing you need to know is how to properly introduce new fish to a new tank while causing as little stress as possible.

Ultimately, stressed-out fish are unhealthy fish. Not only that, but the improper ph, chlorine level, or nitrogen level can actually kill them.

With a little know-how, the good news is that introducing your fish to a tank can be a pretty painless experience for them.

Quick Picks: Great Products To Help Cycle Your Tank

Or, read our full article on some of the best nitrifying bacteria products that you could use in your aquarium.

Here is a fun infographic to help make sense of it all.

How To Cycle A Tank In 24 Hours – Infographic

Infographic - How long to wait before putting fish in new tank.
Infographic – How long to wait before putting fish in new tank.

Further Reading: If It’s Your First Time Cycling A Tank Be Sure To Read Our Guide On How To Cycle Your Aquarium.

Here are our top tips!

Tank Preparation

Before you even head to the store to buy your new fish, there are some steps you can take at home to ensure a safe haven awaiting your new pal.

Step 1: Make sure your tank is the proper size! Too small a tank can lead to a very stressed-out fish.

Step 2: Wash the gravel and any new decorative objects that will be added to the new aquarium. It’s important to wash these with warm water only, as soap and detergents can be toxic to your fish.

Step 3: Fill your tank one-third of the way full of room temperature water from the tap. From here, you’ll need to add a de-chlorinator and water conditioner or something like API Stress Coat to ensure the tap water is treated for fish.

Step 4: Add your plants. These are the 10 best freshwater plants for a beginner aquarium!

Step 5: Connect your filter and begin to pump the water through. This will ensure freshwater is flowing and developing beneficial bacteria before your fish gets to its new home.

Now at this point, you may be wondering.

Can you add fish to a new tank right away?

And if you’re paying attention to this article, the answer is no. The most important step of the process comes next, and in all honesty, it’s a very boring process.

Let’s continue;

Step 6: Wait for the nitrogen cycle to finish.

Yup, that’s it; you need to wait, and once it’s done, your tank is now ready to go!

Before we go on, I want to note that there are ways to cycle a tank in 24 hours, but I’m not covering those options in this article, but I’ll give you a freebie.

The fastest way to cycle your tank would be to take some bio-media or sponge from an existing tank and use it in your new tank’s filter. This way, you’re seeding your new tank with a bunch of beneficial bacteria that can significantly speed up the cycle process.

You’re welcome.

Before You Add Fish In a Tank, Test the Water

The first thing to consider is water. The water your new fish is coming from likely had a controlled ph level.

It’s also important to note the particular fish species you’re dealing with and what their needs are. It’s a good idea to speak with an expert at the store before purchasing and acclimating a fish.

Test your water before adding your fish. You can do this with a conventional water tester available online or at aquarium stores. Your ammonia, nitrites and nitrates, and chlorine should be as close to zero as possible. Your ph should match where your fish is coming from (so don’t forget to ask!)

Give Friendly Bacteria Time to Make Themselves at Home

Bacteria are your friends, and they’re a fish’s friend too!

Helpful bacteria do all sorts of things in an aquarium-like combat ammonia build-up and recycle waste products.

“Cycling” a tank also allows for proper nitrogen levels to balance out as the bacteria make themselves at home.

To speed this process along, there are a few things you can do. Please think of this step as feeding the bacteria their first meal of ammonia.

You can add a small amount of fish flake food, small chunks of raw shrimp, or used filter media and gravel from another established aquarium.

How long does it take for bacteria to establish themselves?

Even with these tricks to speed it up, you should give your tank at least 24 hours to start building up bacteria before adding fish.

How do you know when your tank is ready for fish?

The Nitrogen Cycle is considered not complete until ammonia levels are at 0, and nitrate levels stay below 40 ppm.

And Finally, The Fish!

When adding your fish, you want to treat it like a new and blossoming relationship and take it slow.

Turn off your aquarium light and make sure the temperature is appropriate for your fish species.

Lower the plastic bag you fish came home into the water and let it float. This allows the fish to get used to the new tank in small steps. Do this for 15-30 minutes.

It’s a good idea at this point to test the ph inside the back and compare it to your tank. If they’re drastically different, this will shock your fish and could even kill them!

If the numbers are not the same, Take a measuring cup, add a small (1/4-1/2 cup) amount of the tank water into the bag, and wait at least 15 minutes. Test the ph again and see if the numbers are any closer.

When the ph has a difference of less than 0.1, you’re now ready to introduce your fish!

To do this, carefully lift your fish with a small net out of the plastic bag and quickly transfer it to the tank.

Note: After you’ve added your new fish to the tank you might be wondering when you should start feeding your fish after adding them to a new tank.

How Long Should You Wait Before Putting Fish In A New Tank?

Well, it depends on how fast you progress through each of the steps above.

Even though this may sound like a hassle, and you’re secretly thinking, “well, how bad could it be if I just skipped all that?”

Fish are living things and are therefore highly sensitive to their environments. You risk losing one or all of your fish in a tank if you don’t ensure proper introduction methods and wait long enough to establish a healthy environment.

Do yourself and your fish friends a favor and follow these tips, and you’ll have a happy, healthy aquarium for years to come.

And hey — once you have one healthy aquarium, it’s much easier to create another by transferring bacteria.

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