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How to Quarantine New Fish Properly (in 5 Steps)

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By Lindsey Stanton

Lack of proper quarantine is one of the biggest reasons for failure in the fishkeeping hobby. But now you can have a better chance of success with the knowledge I’m going to share in this post.

I’m pulling back the curtain today on one of the BEST kept fishkeeping secrets of all time: How to quarantine new fish.

So what are you waiting for? Keep reading to find out!

What is Quarantine in Aquarium Fish?

Look: Quarantine is more than an isolation period (unless you got your fish from a trusted breeder or importer directly).

For fish from pet stores, fairs and other places that don’t quarantine, it involves actually treating for all common diseases right off the get-go. And completely.

Sure, there are some sellers out there who hit the fish with a few chemicals for a couple of weeks and call it done. That’s not complete quarantine. Many parasites have a longer lifecycle that can “outrun” shorter treatments, especially at a lower temperature. This can lead to your so-called “quarantined” fish coming down with an issue later and/or infecting your whole collection.

Instead, here’s the way I recommend quarantining to be as thorough as possible.

My Complete 5-Step Quarantine Protocol for All New Fish

Different people have different quarantine methods. This is the one that I have found works best for me for pet store/suspicious fish. I have never lost a fish in quarantine while using this method!

I’ve acquired many fish over the years, some have been quite sick when I received/rescued them. This method never failed to bring them back to health. With that said, very weak, stressed, sickly or little fish may not make it through quarantine no matter what treatments you use. This is normal. Sometimes, everything they’ve been through is just too much.

fish in bag
Image Credit: kao, Shutterstock

Unless the fish comes to you with a specifically confirmed, serious issue that is without question the immediate cause of poor health, I recommend starting with the program below. Here’s how to quarantine new fish properly:

1. Treat External Parasites, Bacteria & Fungus

My all-time favorite quarantine treatment is a product called MinnFinn. I use it on every new fish without exception. I firmly believe it is the gold standard for treating fish diseases after I have seen it work wonders on dozens of my own fish. This is because it’s an all-inclusive, two-part treatment which very quickly and effectively deals with with the following common fish diseases:

  • Flukes
  • Costia
  • Chilodonela
  • Trichodina
  • Fungus
  • Anchor worm
  • External bacterial infections, including mouth rot, columnaris & bacterial gill disease

And the best part? No water changes required to use it.

Tip: A shortcut to reducing the QT time and number of treatments is to give them the MinnFinn bath before you ever add them to the quarantine tank.

This does two things:

  1. Prevents parasites such as flukes from laying eggs in your quarantine tank
  2. Requires fewer treatments, speeding up QT time. Instead of four or five,  you now only have to do one or two, so it is faster and more cost-effective.

I only recommend this for fish you have just purchased from the pet store that do not appear to be sick and stressed. Very stressed fish (as in they look like they are dying) may require a few days to rest up before treatment with this.

If your fish are already added to the tank, you can use four to five treatments of MinnFinn. These treatments are administered every 48 hours.


Goldfish and koi should have a double dose, whereas other fish should have the regular strength doses. (The instructions on the large bottle do not need to be doubled.)

Tip: MinnFinn also works for saltwater/marine fish.

MinnFinn can also eradicate ich, but it may require more than five treatments, as ich has a tricky life cycle highly dependent on temperature. It can only be killed at certain phases in its life cycle, at other times no treatment can kill it without killing your fish.

Ich typically responds better to long-term bath treatments. Salt is the best and safest option for that.

One nice thing is MinnFinn can be used in combination with salt at .3% strength and under. In fact, the salt helps it work even better. This also speeds up QT time.

Note: Some water conditioners such as Prime can neutralize MinnFinn. This may require upping the dose for it to be effective. Up it by 1/4 dose every 5-10 minutes and observe how the fish are responding to ensure the fish aren’t overly stressed. I personally like to do a water change first to get all the Prime out of the water if I have been using it, then treat with a 1/2 dose of regular water conditioner.

2. Follow up with Salt to Kill Any Ich

Contrary to popular belief, ich is not always present in all aquariums. That is a big, fat falsehood made up by fish sellers who do not want to take responsibility for selling sick fish (or don’t understand ich at all).

Deal with potential ich up front in all your new fish during quarantine and you will never have to deal with it again. Nice, right? After all, nce your main display tank has ich, it’s a massive pain to deal with.

Because salt will nuke your plants if you have them, everything exposed to the ichy fish have to be sterilized or destroyed. And if you try to opt for one of the long-term chemical bath treatments, it may not work on stronger strains of ich (not to mention you risk staining your silicone blue)!

If you're terrified of passing on any bugs your new fish may have to your entire aquarium, or just want to be sure you do the quarantine process right, we recommend you read our best-selling book The Truth About Goldfish before you put them in.

The Truth About Goldfish New Edition

It has detailed instructions on a seamless quarantining process and so much more. Your fish will thank you!

So that’s why I do this during quarantine:

Use .2% (7 grams per gallon) for tropical fish like Bettas. Use a stronger solution for goldfish of .5% (19 grams per gallon) for 2 weeks.

Salt should not be combined with ANY other treatments. It also should be dissolved before adding it to the water.

You need to build up the salt concentration gradually in separate doses added 12 hours apart each to avoid shocking the fish. Two separate doses for .2% and 5 separate doses for .5%. Raising the salt level too quickly can result in dehydration of freshwater fish, which can lead to death.

You can use non-iodized sea salt without any anticaking agents or additives, but I prefer to use Himalayan pink sea salt, as it adds many beneficial trace minerals to the water for your fish to assist in healing.

himalayan pink crystal salt

Also, if you raise the temp to 84 degrees Fahrenheit (slowly), you can treat with salt for 10 days to eliminate ich.

3. Deworm Your Fish

Finally, for the last 5 days, it is time to tackle pesky internal parasites.

There’s more than one way you can do this. You can feed Metroplex, Levimasole, Hexshield or 3% Epsom salt feed twice daily for 5 days to get rid of nasty intestinal worms and internal hexamita. Personally, I like the 3% Epsom salt feed option because it is the gentlest on the fish’s system.

Use 1 level tablespoon of Epsom Salt (15 grams) to 500 ML of distilled water. Use an eye dropper to add water to food until the food does not absorb any more. – Recipe from The Truth About Goldfish

Excess magnesium is easily removed from the fish’s body and has no harmful short or long term effects.

Solimo epsom salt


4. Test the Water Daily

Quarantine systems – especially if they aren’t cycled – are very fragile. You can’t really enlist the help of plants without the risk of killing them. And many times, quarantine tanks have quite a lot of fish in them than before they are moved to their real home. The worst part? Stressed or sick fish gas off way more ammonia than healthy ones.

With all these things in mind, I highly recommend testing the water at least once daily for ammonia at a minimum, and nitrite if you are using a biological filter. I use these strips for this.

Large water changes are often required to keep things in check if something is off. Keeping these levels down will help ensure your fish get through quarantine with flying colors.

Pro Tip: Use a healthy amount of activated charcoal (aka carbon) in a filter to keep ammonia and nitrite levels at 0 while the new fish are in quarantine.

5. (Optional) immune system boost

These treatments aren’t a must, but I have found them useful to have around, especially for very stressed fish.

With very stressed fish possibly dealing with internal bacterial infections, it’s time to work on building up their immune system. Not to mention, sometimes those secondary infections are the most lethal after you finally smash the parasites.

To do that, I alternate Microbe-Lift Artemiss and Microbe-Lift Herbtana every 12 hours.


These natural immune stimulants help repair damaged tissue and fend off pathogens, including parasites, bacteria and fungus.

Remember: A strong immune system is your fish’s most powerful protection against disease.

How to Set Up Your Quarantine Tank

Here are some tips for your quarantine tank itself:

  • Tank: The quarantine tank doesn’t have to be anything fancy, and it doesn’t have to follow the same stocking guidelines as your main tank.  It can be an old used tank you found at a thrift store. It can even be a Tupperware tub. Whatever you use, your quarantine tank ideally should be in a separate room to prevent particles from the water traveling through the air and getting into your other tanks. Never share equipment between your QT tank and your other tanks unless it is fully sterilized in between uses. And don’t forget to wash your hands well after interacting with your QT tank.
  • Filter or Airstone: In a best-case scenario, you would use a filter totally pre-cycled with liquid ammonia to keep the water clean.  At the least, it should have an airstone to keep the water oxygenated and the water tested and changed frequently to keep it clean. One trick I use is to use a filter packed with carbon to keep ammonia and nitrite levels down. I don’t like to perform anything other than a 100% water change when treating with salt, as without a salinity meter, it’s hard to keep track of how much salt is in the water. That’s why using carbon has proved to be an easier option for me.
  • Light: It’s important to reduce stress as much as possible after everything your new fish have been through. You’ll want to turn off or reduce lights (if you have them) for the first 24 hours. Bright lights can really stress new fish in a new environment.  Your quarantine tank does not need to have its own light.
  • Plants: Not mandatory by any means, but you can consider adding some live plants to your QT tank, preferably disposable ones as they may not survive the treatment phases to come. I sometimes use Hornwort for my QT tanks as it offers shelter (which greatly reduces new fish stress), supports probiotic bacteria, and helps purify the water. As it grows like crazy, I always have extra on hand for situations like these.

divider fish plants 2

Why Quarantine ALL Your New Fish?

Look: All fish should be quarantined regardless of where you get them from. Even if you get the healthiest, disease-free fish to start with, they’ve been through a lot. The fish just needs to rest up a bit before being introduced to the others.

Some breeders and importers quarantine for you and do it very well. For fish that come from reliable sellers like these, quarantine is very simple. Isolation for 4 weeks minimum. Why 4 weeks? It gives you time to address any issues that could pop up after the stress of shipping and ensure the fish is fully healthy before introducing them to the others.

Your new fish are also really weak and don’t have resistance to whatever pathogens may be in your main system with your other fish. Those pathogens are things your existing fish may be used to living with just fine.


Suspicious Fish

But when your fish comes to you from the pet store – or even from many online retailers who don’t do this- you have to assume they are sick and treat them as such. Because the truth is, they probably will be if they aren’t already.

Maybe you’ve heard  somepeople say you should only treat fish like they are sick if you see signs of a problem. Actually, if you do that, you’re automatically at a disadvantage because goldfish can carry low levels of pathogens without showing any obvious signs of them (it takes a microscope to do that).

By the time they actually start showing signs, many times, it’s too late. You might succeed in battling back the parasites for a time and think victory is yours, only to have your fish succumb to a lethal secondary bacterial infection.

Preventative care is the key to not being stuck in a situation where you are desperately trying shotgun treatments and endangering your entire collection in the process.

Take it from me: one new fish can do a whole lot of damage in a very brief amount of time. Nip potential issues in the bud early on in the game and you will save yourself a ton of stress, money, and potentially heartache.

“Oh No, What if I Didn’t Quarantine and Just Added a New Fish with My Others?”

The new fish and all fish exposed to the new one should go through this protocol. And the sooner you do it, the better. You’d be surprised how quickly a disease outbreak can sweep through your collection, practically overnight. Starting treatment EARLY is key to avoiding a more dangerous situation.

wave tropical divider


Now that you know how to quarantine new fish, I hope this information helps you become a better pet owner.

I’ve shared something that can now empower you to bring home fish from the pet store with a much, much higher chance of survival than could have been possible before. This information also comes in useful if you ever feel sorry for a sickly fish you see there and want to bring it home to nurse it back to health.

Do you have any tips or tricks you use for quarantine? Did you find this information useful?

Let me know what you think when you leave your comment below!

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