ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Successfully Introducing New Fish to Your Old Established Tank

Updated on December 19, 2021

Choose your new fish carefully to avoid mayhem!

Title: Pirahna ~ License: sxu license ~ Photographer: soundman99:
Title: Pirahna ~ License: sxu license ~ Photographer: soundman99:

Select Your Fish Carefully!

Beginning aquarists often start out with a wild mix of fish that don’t get along. That - along with improper tank set-up - is one of the main reasons new aquariums often fail. Once you have your tank properly set up and seasoned and have weathered the initial problems with incompatible fish or fish that just don’t make it for one reason or other, you may find yourself with a tank that has only a few fish that get along well, and you may want to add a few more. Here’s how:

Do your research! Check out my other fish care articles using the links at the end of this article.

Once you have done your research and determined what types of fish would be likely to get along with the fish you have, take a trip to your local fish store. If you do not already have a bottle of the product, Melafix, at home, get some while you are at the fish store. This is an all natural “tonic” that helps with fish stress. It has a pleasant distinctive smell that, I believe, may help keep the fish from realizing new fish have been added.

Select the type and number of fish you want. Bear in mind that you will not want to introduce a lot of new fish at once. This will tend to stir up aggression as well as causing an ammonia spike in the chemistry of your water. This is bad for all of your fish. A good general rule is to have at least a gallon of tank per inch of fish. So don’t put any more fish in your tank than the number that will equal this equation. If you have schooling fish, it is a good idea to get more schooling fish of the same or a similar type. Get fish that are about the same size as the ones you have now. Avoid getting an aggressive fish to add to your tank.

Plan to do a partial water change when you get home with your new fish. Put a couple of gallons of water from the tank into a clean bucket (one that is only used for fish purposes.) Float your new fish, in their bag, in this water for about 10 minutes to get their water to the same temperature as the water in the bucket, then release them into the bucket.

While they are acclimating to the new water, clean and rearrange your tank. Vacuum your gravel and move all of the ornaments and plants around. Take out some old ones and add some new ones if you can. This will confuse your fish and disrupt their habitual hiding places. This should help keep them from being too territorial. Add new water to the tank. Add a dose of Melafix.

Net your new fish by positioning a large net over a clean, empty bucket and gently pouring the water from the bucket that holds your new fish through the net. By doing this, you avoid chasing them around in the bucket and stressing them even more than they already are. Once they are netted, gently introduce them to the tank.

You will be very tempted to stay and watch them and to check on them frequently, but I advise against this. Instead, turn off the light, cover the tank with a blanket or towel, turn off the room light if possible, and leave them alone overnight. If it is dark in the tank, your fish will all go to sleep and wake up the next day in a completely rearranged tank with no territory marked. This will level the playing field so that all of the fish, new and old, can start fresh.


Do the Math!

I always use Melafix for ponds in my fish tanks because it is highly concentrated and more economical. 1 teaspoonful treats 50 gallons when introducing new fish. 2 teaspoonfuls treats 50 gallons when treating injury or illness. It takes 60 drops to equal a teaspoon, so you would use 3 drops per gallon when introducing new fish and 6 drops per gallon when treating injury or illness. When introducing new fish, treat daily for 3 days, then do a quarter tank partial water change. When treating injury or illness, treat daily for a week and do a quarter tank partial water change. Repeat this process if necessary.


This website uses cookies

As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

Show Details
HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
LoginThis is necessary to sign in to the HubPages Service.
Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
AkismetThis is used to detect comment spam. (Privacy Policy)
HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
MavenThis supports the Maven widget and search functionality. (Privacy Policy)
Google AdSenseThis is an ad network. (Privacy Policy)
Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
Index ExchangeThis is an ad network. (Privacy Policy)
SovrnThis is an ad network. (Privacy Policy)
Facebook AdsThis is an ad network. (Privacy Policy)
Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
AppNexusThis is an ad network. (Privacy Policy)
OpenxThis is an ad network. (Privacy Policy)
Rubicon ProjectThis is an ad network. (Privacy Policy)
TripleLiftThis is an ad network. (Privacy Policy)
Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
ClickscoThis is a data management platform studying reader behavior (Privacy Policy)