Quarantine is like wearing your seatbelt, you don’t need to do it at all until you REALLY need to do it, you just don’t know when that will be until it’s too late. So it’s best to just do it all the time.

I used to never quarantine at all. After almost 25 years in the hobby, I had never had an issue with a disease spreading through a tank like wildfire. I had some things pop up here and there, but it was usually just a stressed fish or at most a couple of others. It simply wasn’t worth setting up a whole additional tank to quarantine to prevent a problem I had never had. I didn’t even have issues at the stores I worked at with all sorts of new fish coming in every week. 

This changed when I set up my 220s. I had some community fish in one and everything was fine. I made a trip to visit about five stores in one day and ended up coming home with two boxes of fish. Sure enough, stuff started dying. It started with some guppies that had Columnaris, not unusual for them. However, unlike every time I’d dealt with disease in the past, it spread, and it spread fast. At one point I was pulling 6-10 or more dead fish every day. After longer than it should have taken, I realized it wasn’t going to be the typical flare-up that quickly died off, so I decided to buy meds. I didn’t even know which meds to buy. It had been so long since I had needed to treat for anything, I didn’t have a clue what would work, or even that it was Columnaris at first. I had to do research and was able to get some reliable information, but it wasn’t easy. That’s why I decided to put together a better guide for myself and others and wrote the article on Medications. The stores I went to didn’t have any meds that would treat Columnaris. By this time it was starting to slow down and I was pulling fewer and fewer dead fish each day. I reacted slowly and when I finally did react, I couldn’t get the meds I needed in time. I didn’t lose all the fish, but I lost a lot, probably 60-80% of the fish in the tank. Dozens of tetras, dozens of cories, dozens of guppies, a lot of fish that I really liked were all dead. 

I don’t want this to happen to you. I don’t want to have to deal with it ever again, so I’m changing how I do things and recommend you decide which of the following methods best suits your situation. I recommend following one of the following quarantine methods.
1 – Don’t Quarantine, But Be Prepared
2 – Basic Quarantine
3 – True/Full Quarantine

Don’t Quarantine, But Be Prepared

At the most basic level, you may not actually quarantine at all. In this situation, you choose your fish carefully, but add them directly to the display tank. Most people fall into this category. They do so either because they are new to the hobby and don’t appreciate how quickly a bad disease can spread through a tank, or because they only have the means for one tank, or if they have multiple tanks, they already have them stocked. Whatever the reason, it’s not necessarily a problem. 

In freshwater, almost all the fish are captive-bred which greatly reduces the risk of disease. Even then, diseases can spread. This is especially so when they are moved multiple times and exposed to new fish at every move, which is exactly what happens to them right before you bring them home. This means their arrival is the time they are most susceptible to getting sick. The stress of moving from farm, to wholesaler, to retailer, to your tank is begging for them to get sick and the exposure to something along the way almost guarantees something will be around to take advantage of their weakened immune system which is caused by that stress. If anything, it’s amazing that not every new fish gets sick. 

If this is your method, good luck. You’ll probably be okay, at least until you’re not. The most important thing about this method is that you are prepared if (really when) something does break out. This means having medications on hand ready to go at the first sign of any disease. 

The Best Waste of Money in This Hobby

If this is the method you choose, you should at least have the medications on hand. This is the best waste of money you can ever make in this hobby. I say this because the best-case scenario is that all of the meds are a complete waste of money because your fish never get sick. 

Having the meds on hand is important because any delay at all can completely change the outcome of the disease. Depending on when you notice the first signs, you may have work or other obligations, the local fish store may not have hours that allow you to quickly buy the meds, the store may not stock the right meds or may be out of stock, and even if you order online you will have to wait at least a day or two for delivery. All of this delays when you can even start treatment. By then, you may have already lost fish and the others will be that much worse. When I had this issue, I finally went to Petsmart and Petco and neither one had a single medication that would treat Columnaris. 

Keep Ich-X, E.M. Erythromycin, and General Cure on hand. Having these three will allow you to treat almost anything that will ever possibly show up in your tanks. They are also safe for inverts, plants, and the nitrifying bacteria in the filter. Keep enough on hand to do a full treatment for your largest tank. You don’t want to have enough to get started and then run out before you can properly eradicate the problem. For more information on these meds, please read the Medications article.

Basic Quarantine

As far as true quarantine goes, the most basic level would be to quarantine all new fish for at least two weeks just to make sure nothing pops up. This can save you a lot of headache by avoiding it breaking out in your display tank. At this basic level, you may not even run any sort of preventative treatment. It’s not a great quarantine method, but it’s better than running the risk of adding fish directly to your display. 


Filtration is one of the tricky things about quarantine. You need cycled filter media at minimum. Depending on the filters you use, you can steal a filter cartridge or some biomedia from the filtration on the display. For example, if you have an AquaClear or canister on the display, you can run a smaller AquaClear on the quarantine and when you need to start the quarantine tank, you just borrow some biomedia out of the filter on the display. Another option is to use a sponge filter. You can keep it in the display when not in use on the quarantine tank. Yet another option is to simply run the quarantine HOB filter on the display when not in use for the quarantine. A final option, especially if you are stocking a new tank, is to keep the fish in quarantine until their quarantine is complete, then buy new fish. When you come home with new fish, move the old ones to the display THEN add the new fish to quarantine to prevent the new fish from contaminating the properly and fully quarantined fish. If you don’t remove the old quarantined fish until the day you come home from the store with more fish, then the quarantine tank will remain cycled. 

The Water

In addition to cycled filter media, it’s best not to use 100% brand new tap water in the quarantine. It’s better to use water from the display to fill the quarantine and then refill the display (it’s just a water change as far as the display is concerned). This ensures the water is chemically stable, the right temperature, etc. 

Just like filling the quarantine the first time, it’s good practice to use water from the display to do water changes on the quarantine tank. This keeps their chemistry stable and matching. You may be thinking ‘but no, that’s old water’ and it is, but if you are actually doing enough water changes, even the old water in the display should still be good. This isn’t a requirement, but can help avoid temperature swings and big chemistry changes in the quarantine tank where the fish may already be stressed by the recent moves and being in yet another tank that’s completely new to them. 

Tank Size

Tank size is often underappreciated when it comes to quarantine. As shown above, the tank size used for quarantine can make a big difference. It is vital that it is large enough for the species being quarantined and the amount of fish being quarantined. If you are quarantining small fast fish such as danios, cramming them into a 10-gallon is likely to stress them. This could easily allow disease to break out and possibly end up killing them. This is when quarantine can do more harm than good. Pretend the quarantine tank is their permanent tank, is it large enough? If not, you need to reconsider using that tank to quarantine them. If you can’t upgrade the size of the tank, it may be better off adding them directly to the display and having medications on hand to treat it if something comes up, or even treat the display anyway to prevent something from breaking out. Another option is to use something like a storage tote instead of an actual aquarium. They can provide a lot more volume for less money. It won’t be the most beautiful option, but it’s more important that the quarantine tank does its job than that it looks good.

True Quarantine

A true quarantine will be longer than just a couple of weeks. Zoos and aquariums usually quarantine for at least six months and even then, the time starts over any time any issue comes up. So if four months into quarantine some fish break out with ich, once the ich is treated and completely gone, the six months start over. So if issues come up a couple times, the quarantine can run well over a year. This is why it’s important that the quarantine tank is large enough and decorated in a way that allows the fish to be truly happy. This is also essential in preventing stress which can greatly help in avoiding them getting sick in the first place. 

I’m not saying you have to do a full 6-month quarantine, but you should realize that is what a true quarantine looks like. If you are working with wild caught fish, species that are more sensitive (such as stingrays, discus, etc.), or simply have a lot of money in livestock in your display, I highly encourage you to go with a longer quarantine. It’s the safest way to protect all the livestock in your display. Maybe that means 4 months, or only 2 months, the exact length of time is up to you and may vary depending on the fish being quarantined, new fish that need to come into quarantine, etc.

If you ever add fish to quarantine before the old fish have been in quarantine long enough to go into the display, the fish that were already in quarantine need to start their time over. You can’t move them to the display based on when you got them, you need to run a full quarantine from when the new fish were added to quarantine. 

Preventative/Prophylactic Treatment

In addition to a much longer quarantine, a true quarantine should include preventative treatment with each of the meds listed above to be kept on hand (Ich-X, erythromycin, and General Cure). This will help minimize the risk of any disease ever making it into the display. 

Although the majority of freshwater fish are captive-bred and have been for many generations, there are many exceptions that are still wild-caught. As a general rule, the harder to find a species is, the more likely it is to be wild-caught. For example, you can find neon tetras every week of the year and in any store you ever step foot in. On the other extreme, fish such as gold nugget plecos and flagtail prochilodus are only available occasionally throughout the year. This is usually due to seasonal available for collection in the wild. This limited availability is a big indicator that they are wild-caught. This brings up an important example, fish such as gold nugget plecos. Many fish that can be captive-bred are not captive-bred enough to supply the demand. Generally, if it is captive-bred the store will say so since that is a big selling point. So with species like this, unless you know they are captive-bred, you have to assume they are wild-caught. Any freshwater fish that definitely is or is likely to be wild-caught should be assumed to be wild-caught and therefore receive a full quarantine with treatment for at least internal parasites (General Cure which contains both metronidazole and praziquantel).


If you can’t or choose not to do a full quarantine, you should at least understand the risks and have the medications on hand to treat the illnesses your fish are most likely to come down with. Enough things can go wrong in this hobby, we should at least minimize the things we actually have control over.

Other Articles You May Be Interested In


Disease Control in the Aquarium

How to Acclimate Fish

Stocking an Aquarium

Choosing Fish

Heaters – The Ticking Timebomb in Every Tank