Skip to content

Quarantining Fish

While we wait for the cycle to advance, we're going to take a break and start talking about fish since we're close to being able to add them to the tank. More specifically, we're going to discuss quarantining.


Every fish that you buy and add to your tank has the potential to carry diseases that can be passed on to the other fish in your tank. The best practice is to never add a new fish directly to the tank without a quarantine period.

Quarantine means that you isolate the new fish in a different tank by itself. This lets you observe the new arrival and potentially treat it. A lot of medications should never be added directly to your display tank (DT for short) since they can negatively impact or kill other creatures in that tank. Some medications can be absorbed by your rocks and cause problems down the line.For those reasons, it's best to isolate the new fish in a separate tank, known as the quarantine tank (QT for short).

I know that your immediate reaction will be:

I just spent a bazillion dollars on a new tank and now you're telling me I need another one?

The short answer is yes. In the long run, the QT may save a collection of expensive fish. There's also an emotional toll when all the fish in your tank get sick and start dying one by one: you cannot put a price on that.

The good news is that a QT has different requirements than a DT and can be setup without spending too much.

Quarantine Tank Setup


For a QT, I use an inexpensive 10 gallon tank. Sometimes you can find them for $10. You don't need anything complicated or attractive and a 10 gallon tank doesn't require a sturdy stand: you can put it on a desk or counter top. However, if you plan on getting large fish, you may want to consider a bigger QT.


I like to have a tight fitting, solid lid (as opposed to a mesh lid) for my QT. There are two reasons for this:

  • New fish are going through a lot and can easily decide to jump out of the tank when they're stressed. Even if the fish are not stressed out, some are known jumpers. It's no fun to wake up one morning and find your new fish on the floor. A good lid is a must.

  • A solid lid helps to keep evaporation down to a minimum. This means that we don't need an ATO to keep the water level and salinity stable. Since a QT doesn't require any lights, it's OK to have a solid lid that gets a bit dirty.

For my QT, I got a hinged glass top, which was only $13. This lid has a plastic section in the back that you can cut to run cables.


The QT needs a heater, but it can be something simple and inexpensive. Just keep a couple of things in mind:

  • Glass heaters are a bit fragile and a QT is a place where there may be a lot of activity such nets going in an out to add and remove fish. I prefer something sturdier. My QT has a 50W Cobalt Neo-Therm heater which is expensive at $60 but worth it in my opinion.

  • Some treatments require the QT to have a higher temperature, so don't get a preset heater that can only keep the water at 78°F.

Also, make sure you have a simple thermometer to ensure the heater is working correctly.


The water in the QT needs to be filtered and oxygenated. My filter of choice is a submersible, adjustable filter that only costs 20. It has a few advantages over hang-on-back (HOB for short) filters:

  • Since it can be submerged in the tank, there is no need to make cut-outs on the lid which would otherwise lead to more evaporation.

  • It has an adjustable wand which can be pointed towards the surface to help oxygenate the water. This means that you don't need an air pump to do so and that's one less thing to buy.

  • It comes with a sponge that can help us cycle the QT quickly. If you take the sponge out of the filter and place it in your DT while it is cycling or has already cycled for a week or so, it will be populated with bacteria automatically. You can then transfer the sponge back to the QT for an instant cycle.

  • This filter is very quiet. Being submerged and under the lid, you don't hear anything.

The sponge that is included with this filter may have a bag of carbon inside it. It is important to remove it since it can interfere with some medications.


It is strongly recommended to add a Seachem Ammonia Alert badge to the QT. This will let you know if overfeeding or a lack of bacteria causes a spike in ammonia and gives you an opportunity to address it before the fish suffer. The best way to address it, if it happens is with a large water change which, in this case, can be 50% (5 gallons).

Sand and Hiding Places

The good news is that the QT doesn't need sand. That being said, there are some fish that are not happy without sand. For them, you may need to temporarily add a glass bowl of sand to the QT so it's a good idea to have some on hand. It should be clean and you should throw it away after QT is over for those fish.

Most fish do, however, need hiding places. They need to feel safe and protected during these stressful times. The most cost-effective way to provide them with hiding places is to get a few PVC tees, like the one pictured here, and drop them in the bottom of the tank. Of course, they need to be big enough for your fish but not too big. You can get them in different sizes and it is a good idea to mix them up. They don't absorb medications and can be easily cleaned and dried.


There's no need to put a light over the tank and it is better not to have one in order to avoid algae. But, if the tank is in a completely dark room, you should turn a light on during the day so the fish have some semblance of a day/night cycle.


As you can see, you can setup a basic quarantine tank for around $100. When you compare this to the price of some of your fish, you should conclude that it is well worth it.


There are some alternatives quarantining: some fish stores and some online vendors do it for you. That being said, they still recommend that you at least quarantine the fish yourself for observation when you receive them.

I have had a very good experience with LiveAquaria's Diver Den. They describe their quarantine process thoroughly and all the fish I've received from them were healthy when they arrived. But, of course, that's just my experience.

The quarantine process also serves as recovery time for the fish. Before they are thrown into the display tank with a bunch of other fish competing for food and hiding places, they get to recover from their journey, feel safe and eat as much as they want.

The Quarantine Process

There is a website that is the leading authority on the quarantine process as well as fish diseases and treatment so I'm not going to go into great detail about that here. I'll just refer you to Humble Fish. Everything you need to know is there!

Well, that's enough fun for one day. Let's get back to our cycle.