Red goldfish swimming in darkness.

How to Set Up a Quarantine Tank and How to Quarantine New Fish

Setting up a hospital tank is fairly straightforward, but, depending on what you want to achieve, it has its intricacies. Is it going to be a quarantine tank for new purchases? Or is it a real hospital tank for sick fish?

Maybe your display tank has worms and must stay fallow for a long time to ensure they all are dead?

Each case has its requirements, but here I’ll show you the basics of how to set up a quarantine tank and then we’ll discuss each scenario.

A quarantine fish tank is a bare bottom aquarium with minimal decorations in the form of PVC pipes and fake plants. The water parameters must be maintained with adequate filtration, regular testing, and water changing. Depending on the fish you keep in, a heater may be necessary, too.

Hospital fish tanks don’t need special lights. Fish can live just fine in the ambient light of the room they are in. All the same, it would be better to have a dedicated light so you can see how the quarantined fish are coping with their sickness. Light allows you to spot ich, rotten fins, worms, and other signs of stress or sickness more easily.

If you quarantine newly bought plants, then light is a must for them to stay healthy during the isolation period.

Let’s see in detail how to set up a hospital tank and how to quarantine fish in it.

Quarantine Fish Tank Setup

The basic elements of a hospital tank are the same as of a regular tank sans the substrate:

  • Filtration
  • Heater
  • Thermometer
  • Plastic decoration
  • Light
  • Treated water

Quarantine tanks don’t need substrate because substrates are breeding grounds for bacteria. Normally, that’s a good thing as beneficial bacteria maintain your aquatic ecosystem healthy, but the reality is that they change the water parameters. Yes, even inert substrates do that.

What’s more, the substrate can become home to worms or the nasty ich that replicates on the bottom. A bare bottom tank is much more easy to clean and to clean well. That matters when dealing with ailments.

Now, let’s examine each element of the quarantine tank.

Hospital Tank Size

The size of your quarantine tank will depend on the size and number of fish you want to isolate there. Generally speaking, bigger is better but that’s not always a realistic option.

Your hospital tank can be as small as 40 liters or 10 gallons, but 80 liters or 20 gallons is a much safer choice. Even without substrate, a larger tank will be a more stable environment. Temperature won’t fluctuate as quickly if the heater malfunctions, while more water reduces the chance of deadly ammonia spikes.

Ideally, you should have two quarantine tanks, but one is infinitely better than none.

Of course, if your main tank is small or the fish you are keeping aren’t oscars, large cichlids, angelfish, or big goldfish, you can make do with a smaller quarantine tank. Be more careful with it by cleaning it and testing it regularly.

You can also use a plastic box as a hospital tank. Glass aquariums are heavier, break more easily, and cost more. If you don’t maintain a quarantine tank at all times, a plastic box will do just fine. Its lid must be drilled so that air reaches the water surface. Other than that, the setup principles are exactly the same.


Quarantine tanks can do with good aeration and filtration. They must be kept clean and oxygen helps deal with many ailments like ich. Also, sick fish may have problems breathing so providing high levels of oxygen is beneficial.

Daily or bi-daily water changes could work as a filter, in case you don’t have one, but a simple sponge filter often is enough of a solution.

Can You Use Filter Media from Another Tank?

To kickstart the cycling of a new hospital tank, you can introduce filter media from an existing tank. Filter sponges, pebbles, and other filling house huge colonies of beneficial bacteria that help massively with the nitrogen cycle.

The only time you should not use media from an existing tank is when said tank is infected with disease or parasites. If you are isolating fish from a sick tank and need to start a hospital tank quickly, you should get an ampule with beneficial bacteria from the local fish store.

Alternatively, if your local fish store is nice and clean, you can ask them for filter media.

Heater for Quarantine Tank

Heater is necessary in certain parts of the world and for tropical species. Supply your hospital tank with one, whether for quarantining new fish or isolating sick individuals.

What’s more, high temperatures help deal with certain ailments. Increasing the water temperature to 28°C or 82°F shortens the ich lifecycle and is one of the recommended steps in combating this disease.

When transferring sick fish to a hospital tank, make sure its temperature matches the one from the main tank. Then, if needed, increase it to 28°C/82°F, as long as the fish you put there can tolerate such warm water.


A thermometer is necessary in any tank. It doesn’t really matter whether it is a digital or analog one.

However, it is a good idea to have the same model and brand as in the main tank so you get the same readings.

Decoration for Quarantine Tank

Adding some decoration to a hospital tank helps reduce stress in fish by providing hiding spaces.

Go for plastic decoration. PVC pipes are the best solution because they are very affordable and many species like plecos and other bottom dwellers love hiding in caves. A couple of pieces usually suffice.

You can add plastic plants, too. They provide shelter to fish that swim higher in the water column. Fake plants are excellent for hospital tanks, so I always keep a few handy.

The reason why plastic decoration works so well for quarantine tanks lies in the fact that plastic doesn’t absorb anything. Porous rocks are a bit like sponges. Any medication used will stick there and will be released in the water column over time.

The same goes for driftwood. It has many health benefits, including the release of tannins that help fish immune systems massively, but driftwood has no place in a hospital tank. It will absorb any medication you administer. That’s dangerous in consecutive medication sessions as the concentration of medicaments in the water column may rise to critical levels.

Pipes and plastic plants are the safest options for hospital tank decoration.

Light for Quarantine Tanks

If you have only fish in the quarantine tank, any light will do. Fish can live in darkness, but a desiccated aquarium light will help you monitor their health.

However, if you quarantine newly bought plants, you’d have to provide them with adequate lighting. They won’t mind much 2-3 days with subpar light, but the proper quarantine period should be at least two weeks (ideally, four). Poor lighting is likely to cause melting in your plants.

One way to not overspend on lighting equipment is to maintain a small quarantine tank for plants. They don’t need much space and with regular water changes and possibly a bit of fertilizer they will be just fine.

Treated Aquarium Water

The water added to your quarantine tank should be dechlorinated, at the very least. Chlorine evaporates from water within 24 hours. Keeping the water you want to add to the tank in an open container for 24 hours does the trick.

A faster and safer approach is using water conditioners like Seachem Prime that remove metals and ammonia from the water, too.

Basically, treat the water the same way you do for your main tank.

The only thing to avoid is pouring water from the main tank into the hospital tank, in case the former is infected. Also, when buying new fish or plants, accustom them to the water conditions of the quarantine tank but never add the water from the store to the isolation aquarium.

How Long You Should Quarantine New Fish

New fish should be quarantined for at least four weeks. Whatever fish you buy — danio, guppy, goldfish, betta — should be isolated for a month or more.

Now, 4-6 weeks is long, indeed. If you are buying fish from a trusted source (and the fish isn’t very rare or expensive), you could shorten it, but the risk is always there. Most diseases will manifest in a couple of weeks, but worms may take longer.

Should You Medicate New Fish During Quarantine?

There is a serious debate about whether you should run a preventive medicamentose treatment.

The idea behind quarantining new fish is observation in isolation. That’s why the new fish should stay in a hospital tank for a month minimum.

Administering meds, especially a trio, is often dangerous without previous experience and can lead to fish death. Knowing what each medication does and how it does it is essential. Any time a fish shows signs of sickness in a quarantine tank, you should try to diagnose the ailment and treat it.

Arguably, salt is the best preventative medication that will take care of many parasites and even bacterial infections. Low dosages — 5 grams per 10 liters — of the right type of salt are safe for virtually any fish and will help with parasites. Salt is affordable and doesn’t spoil, so it is a good medication to have but it also requires care and understanding.

Use the quarantine to observe your new fish (or plants) and don’t medicate without a reason. If you need to shorten the quarantine period for some reason, salt is a safe-ish way to go about it.

As a sidenote, never use salt in a tank with snails.

Should You Feed Fish During Quarantine?

New fish must be fed well.

Many new additions to fish stores arrive malnourished. They often have just arrived at the fish shop after a long, stressful haul during which they probably hadn’t been fed.

That’s another great thing about having a hospital tank for your new danios. You can feed them as much as needed during quarantine, without overfeeding your main aquarium. Feeding your fish too much isn’t a good idea in the long run, but new fish should gain weight.

You may even get lucky. If you feed a school of danios for a few weeks with a lot of high-protein food, they may start breeding.

Make Your First Quarantine Tank!

While having an aquarium for sick or new fish is not an absolute must, knowing how to set up a quarantine tank is essential. Actually setting up one should be your first investment in the fishkeeping hobby, right after you finish stocking the main tank. Quarantine tanks save a lot of trouble down the road. Pest snails are hard enough to remove, but they pale in comparison with fish diseases and parasite infection

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