How to Set Up a Hospital Tank For Your Fish

A hospital tank is an aquarium that is set up in order to treat sick or injured fish. 

It’s kept separate from the main display tank so that afflicted fish can be isolated from their tank mates for treatment.

This serves several purposes: 

  • Keeps disease from spreading to healthy fish
  • Lets injured fish avoid aggression from tank mates
  • Reduces the amount of meds that need to be used because of the smaller water volume 
  • Small simple setups make frequent water changes less of a hassle

Here’s how to set on up the right way.

How to Set Up a Hospital Tank

Goldfish in hospital tank

The biggest thing to remember about hospital tanks is that they don’t have to be fancy. This is just a barebones setup that’s for treating fish away from the display tank.

Some aquarists keep dedicated hospital tanks, but often, these setups have to be put together on the fly.

The Tank Itself

You don’t even need to actually use a glass aquarium when you set up a hospital tank. You can use a plastic storage tote if that’s what you’ve got on hand. 

In a pinch, you can even use a bucket.

As long as it’s clean and can support the weight of the water, that’s all you need. 

If you need to add a heater to a plastic tote, make absolutely sure the heating element doesn’t touch the side of the tote, possibly melting it.

Tank Size

Since this is a temporary home for your sick or injured fish, don’t worry about getting a giant tank. It’s fine to get something that’s at or a little below the minimum tank size for that species of fish.

For example, if normally it’s recommended for a species to be kept in at least a 10 gallon (39 liter) aquarium, it’s ok if your hospital tank is only 5-7 gallons (19-32 liters), the fish won’t be kept in this tank long-term.

Often, having a smaller setup can make it easier to treat sick fish and keep an eye on them.

Also, aquarium medications can be very costly. The smaller the volume of water you have to treat, the less expensive the treatment will be.


Figuring out filtration can be the hardest part of setting up a hospital tank. Usually, hospital tanks are either set up on the fly or are left empty for long periods of time.

Either way, you’re dealing with an uncycled aquarium. 

If you’re not familiar with the Aquarium Nitrogen Cycle, please, see our in-depth article, here.

Without the needed beneficial bacteria in the filter of the hospital tank, you can end up with dangerous ammonia spikes that can stress and kill your fish.

You have three main options:

Seasoned biomedia – you can add some biomedia that’s been in the filter of your established tank. This is more for infections, like ich, where treatment will not destroy beneficial bacteria.


  • Seasoned filter media is loaded with beneficial bacteria from your established filter.


  • There is a risk of cross contamination when you move anything from the established tank to the hospital tank.
  • Some medications will kill the beneficial bacteria, making adding seasoned filter media meaningless.

Chemical filter media – you can add chemical filter media that will remove ammonia and/or other waste byproducts from the water column. Zeolite will remove ammonia and Seachem Purigen will remove ammonia, nitrite and nitrate.


  • No chance of cross contamination
  • Can remove waste products without beneficial bacteria


  • Some forms of chemical filtration, like Seachem Purigen, will remove medications from the water.

Daily water changes – if neither seasoned media nor chemical media makes sense in your situation, then daily water changes to remove wastes. Perform a 70%-80% water change each day.

I generally recommend that you use a simple air driven sponge filter in a hospital tank. They do a great job of aerating the tank and can provide excellent mechanical and biological filtration. 

They’re also cheap and easy to set up. And they produce a gentle current that’s not hard for sick fish to swim against.

If you plan on using any sort of chemical media, there are sponge filters that have compartments for adding ceramic biomedia. You could fill one or both compartments with zeolite or Purigen. 

Please, see our detailed article about sponge filters, here.


Whether or not you need a heater is determined by what kind of fish you are going to place in the tank.

For example, if it was a tropical fish, like an angelfish, you absolutely would need a heater.

But, if it was a coldwater fish, like a goldfish, a heater would not be needed.

I would highly recommend using a heater that has a guard over the heating element. Sick or injured fish might accidentally lay against a heater, potentially giving themselves a severe burn. Please, see our detailed article about aquarium heaters, here.


You don’t have to add any kind of lighting onto a hospital tank. Ambient light in the room will be enough for the fish.

If needed, you can shine a flashlight into the tank to get a close look at the fish.

If you really just want a light for the tank out of principle, a cheap LED fixture will do the trick.


You can just skip the substrate altogether in a hospital tank. It’s so much easier to vacuum out a bare bottom tank.

Just a few swipes of the gravel vac will remove solid wastes, making water changes quick and painless.

Plants and Decor

Again, this is not something where you need to go nuts.

I do think that fish need a little something in the tank, like a plastic plant or a simple cave for shy fish, like plecos.

A small amount of decor gives fish a place to hide and a feeling of security.

Keep in mind, some medications, like methylene blue, can act as a dye. So, just grab something cheap and easy to clean.

Final Thoughts

Sometimes, things don’t go right. It happens to everybody in this hobby, sooner or later. Fish get sick sometimes. Or there’s an aggressive bully in the tank that beats up a hapless victim.

Being able to set up a hospital tank can prevent disease from spreading to healthy fish and/or let an injured fish recuperate away from any aggression from tank mates.

Hospital tanks do not need to be elaborate or fancy. This is just an emergency holding area for treatment.

Sick fish often require a lot of water changes. A simple setup will be quick and easy to clean. 

I hope you find this article helpful.

I wish you and your fish the very best!

Katherine Morgan
Katherine Morgan

Hey, there! I'm Katherine from Northwest Florida. An aquarium specialist, I've kept tanks for over two decades, enjoy experimenting with low-tech planted setups and an avid South American cichlid enthusiast.

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