How to Quarantine Fish the Easy Way

Many beginners may not know this, but one of the easiest ways to stop your fish from getting sick is to set up a quarantine tank. This separate aquarium is used to temporarily hold newly purchased fish or ailing animals that need a quiet environment to heal. By putting them in isolation, it allows you to closely observe their health, administer any treatments, and prevent illnesses from spreading. Once they are completely healthy and disease-free, you can safely add them to your main display tank without infecting the existing fish.

Materials for the Hospital Tank

• Clear plastic tub or aquarium with a lid
• Aquarium filter with low flow, like a sponge filter
• Aquarium heater and thermometer
• Aquarium decorations and hides
• Water conditioner
• Trio of quarantine medications (includes Mardel Maracyn, Aquarium Solutions Ich-X, and Fritz ParaCleanse)

How to Set Up a Quarantine Fish Tank

1. To avoid cross contamination, place the quarantine tank in a different room away from your main display tanks if possible. (Other best practices include using a separate set of nets and siphons for the quarantine setup and washing your hands after each time you touch the quarantine fish tank.)
2. If you are using a plastic tub, prepare the lid by drilling some holes for air flow and cutting a small rectangle on the side for power cables and airline tubing to pass through. Another optional step is to mark up the side of the tub with 1-gallon measurement lines to help make water changes and medicine dosing easier.

A clear plastic container can be used as a cheap quarantine setup. Cut or drill some holes in the lid to allow for easy equipment installation and better air flow. 

3. Fill the hospital tank with water and add water conditioner.
4. Install the aquarium filter and heater, and add fish tank ornaments to give the animals some shelter. There is no need to use gravel or other substrate because a bare bottom setup allows you to easily clean the hospital tank and examine the fish’s waste if needed.

Use a bare bottom tank with aquarium decorations to provide plenty of cover. Sick fish often want to hide, so the extra shelters will make them feel more comfortable.

5. Add the fish, observe their physical appearance and behavior, and treat with medication if needed. Remove any chemical filtration (like activated carbon) and UV sterilizers before adding medicines.
   1. If your fish are already sick and you can identify the disease, treat the fish with the specific medication for that illness and follow the manufacturer’s instructions on the packaging. If you are not sure which disease they have, follow the instructions in this article.
   2. If you purchased fish from a local fish store or breeder that you trust to have healthy animals, feed and observe the fish for a couple days. If you detect an illness, see Step 5a above. If you do not see any symptoms, consider proactively treating them with ParaCleanse (as per the manufacturer’s instructions) to clear out any remaining internal parasites that are harder to spot.
   3. If you bought new fish from an online retailer, pet store chain, or untested source, proactively treat them with the quarantine medication trio. These medicines contain a blend of antibiotic, antifungal, and anti-parasitic active ingredients that are safe for scaleless fish, fry, shrimp, snails, live plants, and beneficial bacteria. Dose 1 packet of Maracyn, 1 packet of ParaCleanse, and 1 teaspoon (5 ml) of Ich-X for every 10 gallons of water. Let the medication soak in the water for 7 days without feeding the fish.

Description of quarantine medication trio

6. After treatment is completed, do regular water changes each week to gradually remove the medications over time. Help the fish to build up their immune systems by feeding high quality fish food like frozen foods, which are nutritionally dense and easy to clean up.
7. We recommend quarantining most new fish for 4-6 weeks since the last disease symptom or death was seen. If you want to be extra safe, consider adding two healthy fish from your main display tank to the fish hospital tank and see if they get sick. If everyone remains well, you can finally release the isolated fish from quarantine.
8. Once quarantine is done, clean the hospital tank setup and store everything dry. If you plan on purchasing more fish in the near future, just leave everything running so that it will be ready for the next batch.

Frequently Asked Questions about Fish Quarantine

How big does a quarantine tank need to be? Since it is only a temporary setup, a quarantine tank does not need to be as big as the recommended size for the fish to permanently live in. A hospital tank with less water volume also allows you to use less medication when treating the fish.

How do you keep a quarantine tank cycled? The easiest way is to run a spare sponge filter (or extra filter media in a hang-on-back filter) in one of your display aquariums. Whenever you need to quarantine some fish, move that extra sponge filter or filter media to the hospital tank so it will bring over lots of beneficial bacteria to help purify the water. After the quarantine period is complete, put the sponge filter or filter media back in your main tank. To find out what is cycling and how to cycle an aquarium, see our full article here.

Run an extra sponge filter or filter media in an established tank, and then use it to bring beneficial bacteria to the hospital tank when needed.

Can I quarantine fish in a bucket? Yes, any clean, food-safe container that is large enough will work in an emergency. However, we recommend using a container with clear sides so that you can easily view the fish from all angles to see if their health is improving or worsening.

Should you quarantine shrimp and snails? Dwarf shrimp can sometimes carry diseases, especially if purchased directly from importers, so if you are bringing in a batch to add to an existing colony, consider putting them in quarantine first to observe their condition. In our experience, snails rarely seem to carry illnesses, so we usually skip the quarantine step and add them directly to our aquariums.

Do I have to quarantine my first fish? If you are setting up your first tank, you can theoretically add new fish directly into the aquarium without setting up a separate quarantine tank since there are no existing animals to protect. One situation where you might want to use a separate hospital fish tank is if your aquarium is very large and the fish are small enough to go in a scaled-down quarantine setup. It will cost less money to dose medication in a smaller volume of water rather than an entire display tank.

Another instance would be if your main aquarium is full of live plants or snails. In cases where the quarantine med trio does not seem to be effective, we often turn to aquarium salt as a second line of defense. Since plants and snails generally do not like high concentrations of salt, it would be best to move your fish to another container for treatment.

What should I use to treat fish if I can’t buy the quarantine med trio? We recommend using aquarium salt – a cheap and widely available “medicine” that is quite effective for broad-spectrum treatment of bacteria, fungus, and external parasites. However, it is not safe for aquatic plants, snails, and certain fish like anchor catfish. For more information, follow the dosage instructions in our aquarium salt article.