How to Quarantine New Fish

How to Quarantine New Fish

When introducing new fish, it is important to quarantine them. Here's the how's and why's of healthy fish acclimation.

New fish may have parasites, pathogens, or viruses-- without displaying any signs. When you introduce a new unquarantined fish into your pond, you endanger the health of your existing pond fish, who may not have immunity.

Fish acquired from reputable hatcheries and fish markets are usually free of dangerous infections. If you have acquired your fish from local aquarists on multiple occasions and have not witnessed any signs of disease, you may simply acclimate the fish before putting them into your pond. Any imported fish sold in local fish stores have presumably been quarantined.

Quarantine Tank Setup

You will need a separate holding or quarantine tank for your new fish. It can be much smaller than your pond: anywhere from 100 to 500 gallons is a reasonable size. 

In addition to the tank, you will need the following equipment:

  • Pond salt (Rock or aquarium salt, NOT table salt. Table salt has caking agents, which can kill your fish.)
  • Filter
  • Air pump with air stones
  • Cover/Net
  • Test kits for pH, salinity, ammonia, and nitrite
  • Water thermometer

The tanks utilized do not need to be top of the line or anything fancy; they simply need to be reliable. In place of glass tanks, sturdy plastic drums, water troughs, show tubs, and even inflatable pools can be used. Before introducing the fish, thoroughly sanitize them.

Rubbermaid Commerical Stock Tank

The tank's pump and filter should be appropriately sized. A good air pump with air stones is also required to aerate the quarantine tank.

You should keep a close eye on the water quality as well as the behavior of the fish. Obtaining a testing kit to test the levels in the tank is critical.

Pond salt is also an essential component of the quarantine process. Pond salt or aquarium salt aids in the prevention of parasites, the healing of wounds, and the production of a slime coat that protects fish from parasites, illnesses, and viruses.

Finally, make sure the tank(s) have a porous net or covering. This is critical since stressed fish tend to scare quickly and may seek to escape.

Quarantine Process

  1. Set up the tank. This includes getting the filter set up and adding 0.5-1% (one pound salt per 100 gallons of water) to the water.
  2. Acclimate the new fish by floating the fish in their bag. It takes about 15-20 minutes for the water temperature in the bag to match the pond water temperature.
  3. Once the temperatures are just about identical, carefully open the bag and release the fish.
  4. Cover the quarantine tank with net.
  5. (Optional) Use a piece of plastic or styrofoam over the net so the koi have some shade and coverage. This will allow the koi to feel safer in its new temporary home.
  6. Test the water daily for the first week. Test for: temperature with a pond thermometer, pH, ammonia, nitrite and salinity. If the samples are stable after the first week, you may switch to testing every few days.
  7. Don't feed them for a few days until they have become used to their new surroundings
  8. Perform a 25% water change weekly.
  9. Keep an eye on the fish. They should swim around the tank without scratching its side (also known as flashing).
  10. If you feel like your fish are healthy after 2-3 weeks, you can move them out to the pond; re-acclimating them if the water parameters for the pond and the quarantine tank are too different. 


  • Quarantine your fish for at least 2 weeks
  • Do not introduce sick fish into your pond even after the quarantine period is over.
  • Acclimate your fish when adding to your quarantine tank to your pond. This will help prevent the fish to go into shock from temperature change.