First Tank Guide Tank Logo
First Tank Guide Home

Buying New Fish

How Frequently Should New Fish Be Introduced to Your New Fish Tank?

(The First Tank Guide)

Once you get your fish tank started, you are undoubtedly anxious to get fish for the aquarium. After all, having an empty aquarium sitting in your room isn't particularly interesting or engaging. And this can be even more frustrating if you have a lot of money invested in the fish tank and aquarium equipment, or if there is something about the fish tank that is, shall we say, "less than ideal," like noise from a pump or space taken up in your home.

Your First Fish

There's some good news!

You can get your first fish to start the cycling process very soon after getting your fish tank set up. You only really need to wait for the temperature in the aquarium to be stable - and in the right range - and to be sure that all the equipment is operating correctly and that nothing leaks. This can sometimes be accomplished in a few hours, but you may want to wait a couple of days, or at least overnight.

Once you are sure that nothing leaks, that all your aquarium equipment is operating correctly, and that the temperature is both stable and in the correct temperature range for the fish you want to keep, you are ready to purchase your first fish, introduce them to your fish tank, and start the cycling process.

When to Get More Fish

You do not want to add any additional fish to your fish tank until the aquarium has completely cycled - a process that generally takes 6-8 weeks.

This means that you need to wait at least six weeks after introducing your first fish before you consider introducing any additional fish to your fish tank.

The only exception to this would be if you unfortunately lose all the fish you introduced to your fish tank as your first fish.

How Many New Fish to Get

When you are getting new fish for your fish tank, there are a few guidelines that will help prevent problems with the fish due to the increase in population.

First, you do not want to add more than about 1 inch (about 2.5cm) of fish for every ten gallons (about 40 liters) of aquarium volume at any one time. Adding more fish than this can be a strain on the biological filter and can cause the fish tank to partially cycle again as the biological filter tries to catch up with the additional waste now in the fish tank.

Similarly, you do not want to more than double the population of the fish tank at any one time. This is for the same reasons. Even doubling the aquarium population puts a strain on the biological filter and can cause the fish tank to partially cycle again.

Although partially cycling is not as stressful to the fish, and usually is much faster the the initial cycling process, it can still lead to ammonia stress or ammonia poisoning and 'new tank syndrome' - even in old, well established aquariums.

How Often to Get New Fish

In addition to limiting the number of fish you get at any one time, you also want to limit the frequency at which you get fish.

You generally want to wait at least two weeks between introducing new additions to your fish tank. This gives time for the biological filter to get caught up again. This time also allows the new fish to get used to the fish tank, and the older, more established fish to get used to the new additions to your fish tank.

In addition, this wait also gives time for any disease introduced by the new fish to rear its ugly head so you can deal with that issue without also having the stresses of additional fish being added to the fish tank.

You never want to introduce new fish to your fish tank while a disease is evident or within four weeks after you have completed treatment of a disease.

Waiting two weeks or more between introductions of new fish to your fish tank also gives the last group of new additions plenty of time to recover from the stress of being moved. This will reduce their risk of catching any illness that may be inadvertently brought along by the next bunch of new additions.

When to Stop Getting New Fish

Of course, as important as knowing when to get new fish, it is also important to know when to stop getting new fish.

You want to monitor your aquarium population and make sure you have room for additional fish before purchasing any additional fish. You also want to research the size and compatibility of the fish you are considering before getting them.

"Your site has made my fish knowledge go from, "What the heck?" to, "Yeah, I knew that already." Thanks so much Keith! A 12 year old girl couldn't have had any better help. My father also read your site and it seems that it's appropriate for all ages. I will definitely recommend this place to all fish owners, beginner to expert, young to over the hill. Thanks again."
June 17, 2003
More Comments
"Thank you for your GREAT website and your willingness to assist others. That's very thoughtful and quite awesome!"
January 28, 2017
More Comments