How To Introduce New Fish into a Tropical Fish Tank

How To Introduce New Fish into a Tropical Fish Tank

Tropical fish are some of the most beautiful in the world and adding an aquarium to a room is an attractive and often mesmerising feature. What's more it's a lot of fun setting up the perfect environment for fish to live in, and there are some amazing aquarium designs around these days, whether more traditional or state of the art contemporary ones. If you already have a tank with fish in it and want to add a few more to the environment, there are certain things you need to bear in mind because introducing new fish into an established tank has to be one of the riskiest things a fish keeper might think about doing.

Things to Consider Before Introducing Any New Fish

Your tank might be just perfect with a harmonious and well balanced environment for your tropical fish to live in, so if you are tempted to add more fish to it, before doing so you should consider the following points:

  • It may just upset your aquarium's ecosystem
  • New fish may cause conflict in the tank
  • The new fish may introduce some disease organisms with them

These three things may put you off the idea of introducing new tropical fish into your tank, but if you follow a few basic rules – it is possible to do without creating more problems for yourself. The first thing is to avoid being tempted to put your new fish straight into an existing tank. If you have just lost a few fish, then you need to make sure your tank's ecosystem is stable as well as disease free. Secondly, you need to choose a time when your existing fish are happy and stress free before you put new ones in.

However, some species of fish tend stress out if there are not enough in a shoal which means you need to introduce more fish as soon as you can, but as safely as you can too. Then of course, you need to make sure your new fish are introduced without any stress to them too – the transition has to be as easy as possible for them and at a time when your existing fish are happy, healthy and content.

Choosing Healthy Disease Free Fish

Needless to say, when choosing new tropical fish, you need to choose healthy specimens sourced from a reputable dealer. The rule of thumb is to look for bright colours and undamaged, pert fins. If you notice any tatters on their fins or they appear to have any sort of wound, then best leave them alone and look for some other fish elsewhere. Even so, you would need to treat any new fish you get as soon as you get them home and before you add them to your existing aquarium.

The Importance of an Isolation Tank

Before placing your new tropical fish in your main tank, you should let them spend a minimum of two weeks in an isolation tank. However, as most aquarium fish are kept in pretty crowded conditions in shops and breeders, it can prove to be a little stressful for them if they suddenly find themselves on their own, which is why it's a good idea to place plants in the isolation tank so the new fish can hide in them if they want to. The less stress a fish has to go through, the healthier and happier they will be.

Treating Your Fish in Isolation

During the time your new fish are in their isolation tank is your ideal chance to treat them with a general purpose antibiotic. You should also treat them with some type of anti-parasite solution – one very good one is called Paraguard which has the added bonus of helping fish build up a healthier protective coating of their natural mucus. The most important thing when treating fish with any of these medications is to ensure you finish the entire course before you transfer the new fish to your main aquarium – no matter how healthy they appear to be.

The other advantage of placing new fish in an isolation tank is that it gives them the time to adjust to the sort of food you normally feed your fish and which they might not be used to. It can prove rather difficult to get new fish used to a change of food if they are in a busy or maybe aggressive environment of a main aquarium.

Making Sure There's No Conflict

You might have a happy balance and the most gregarious fish in your aquarium but even they will be wary of strange, new fish that suddenly appear. It could be a stressful time for your existing fish as well as the new arrivals. However, there are certain things you can do that can help reduce the risk of any conflict happening which includes the following:

It's a good idea to have an isolation tank next to your main aquarium so the fish can see each other and as such get used to one another before they actually meet in the flesh

Another good idea is to move a few rocks around in your existing aquarium so the fish you already have in there are not quite so sure of themselves which will help to make them less territorial

If you have females then place them in your existing aquarium before you add any males – females will always be a lot more welcome. If you are introducing a group of fish, put the males in last so they don't have such an impact on your existing fish

As soon as you've introduced the new fish into the aquarium, give all your fish a surprise feed which will help distract your existing fish from the fact new fish are in their tank. The thing to avoid at all costs is introducing new fish when it's close to meal times – tensions will be high and the risk of conflict will therefore be greater.

Making Sure Your Aquarium is Stable

Adding new fish to an aquarium means making more frequent water tests so that the nitrogen cycle remains healthy and stable. This is why it's important to only introduce new fish in small numbers as it avoids making too much of an impact on the stability of the tank's environment and therefore putting your existing fish at risk. Another way to reduce any risk of pollution issues is to treat the whole aquarium with a compound such as Big Fish Fresh Start. The bonus of the compound is it will have a stabilising effect on the overall health of all your fish.


The key to successfully adding new tropical fish into an existing aquarium, is to show a lot of patience and not be tempted to rush things. You also need to be thorough when you do any water tests and then you need to be diligent when observing your fish after they have been introduced into your main tank. If you keep to the basic rules, everything should go well and all that's left for you to do is sit back and enjoy your aquarium and the new fish you introduced into it.



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