quarantine tank not in use

What do you do with your quarantine tank when it is empty?

One common question I get is this:

What do you do with your quarantine tank in between fish or corals, when it is empty?

It’s a great question–and it shows some progressive thinking.

As responsible aquarium owners, we set up and use a quarantine tank and proper quarantine techniques and procedures to:

  • Observe our new purchases to ensure they are healthy
  • Give them time to acclimate to our care and fatten up before being added to the display tank
  • Prevent transmission of disease or parasites to the main tank
  • Allow for the easy treatment of any issues that might come up.

Quarantine makes sense to most rational aquarium owners, but it is only sporadically used, for a number of reasons. The most common reason I hear is that people simply don’t want to wait. It’s painful to wait 4 plus weeks to add that prized animal to your display tank.

People are also unsure what to do with their quarantine tanks when they are in between caring for and quarantining new animals. They know you have to cycle the tank (biological filter) before adding the fish or corals to the quarantine…but what happens after that first fish or coral?

If you’re not adding another animal right away–do you keep the QT running or shut it down?

quarantine tank not in use

Personally, I shut it down, unless I have plans to add something else soon. For a few reasons, I like to shut the tank down.

  • That way I don’t have to keep the biological filter active, with nothing in the tank
  • I don’t waste electricity

But I do this in a way that I won’t have to wait and cycle the tank again, from scratch, once I do want to set it back up again. I do this by keeping a spare sponge filter in my sump. I keep two sponges in there, actually. Then, I have an active, fully cycled biological filter ready to go anytime I need it.

After QT is over, I clean and dry out the tank and sponge filter in between uses, to prevent cross-contamination of any pests that might be in the quarantine. But I always have that second sponge ready, in case I need to put a fish in a hospital tank or if I have another spontaneous purchase.

My quarantine protocol

  1. Test the display tank water to make sure it’s suitable
  2. Plan and execute a water change large enough to fill 75% of the QT tank with display tank water
  3. Fill the remaining 25% with newly made tank water
  4. Add a sponge filter (that I keep in my sump) to the tank–voila–instantly cycled quarantine tank
  5. Keep the fish in QT for at least 28 days. More, if I’m being patient and can muster the mental strength.
  6. After adding the animal to the display tank, clean the QT with freshwater (including the sponge filter) and dry it out
  7. Repeat step 1 to get it ready for the next animal


You could keep the quarantine tank up and running, but you’d be wasting electricity, creating extra noise in your house, increasing your maintenance–and to be honest, you’d never really be sure if your filter was ‘ready’ to handle the addition of a new fish.

Without sufficient nutrients to keep the filter going, the population would die back, in between uses.

Stashing an extra sponge filter or two in the sump is how I am able to shut down my quarantine tank in between new additions to the tank. What do you do?






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