Transferring Fish – Pond to Pond

koi pond backyard water feature

Transferring Fish 

Whether you are transferring fish from a holding tank back to the pond after a cleanout or from one pond to another, there are several things that need to be considered for the safety of the fish.

  • difference in water temperature
  • difference in pH in water
  • chlorine

Temperature Differences and water makeup

The water temperature difference between where the fish are and where they are going must be 5 degrees or less.  Keep this in mind when doing a mid-summer cleanout in Colorado because the water from the hose is much colder than a pond in the middle of a hot July.  Always add de-chlorinator when putting fish in water from the hose.  Here are some options –

  1. Bag fish and let them float in the the new water for 15 to 30 minutes to allow temperature to even out.  Every few minutes give a splash into the bag of the new water.  This will help the temperature come to equality as well as slowly change the pH in the water they are in. When the water temperature is the same or under 5 degrees you can safely transfer the fish.
  2. Fill up the new pond and let it sit for 2 days to a week.  This will allow the air temperature to bring the pond up to normal temperatures.  It will also allow chlorine to evaporate and give you a change to add beneficial bacteria to the system several times before the fish even get into it, establishing the ecosystem.


When adding new fish to your existing pond population, isolating new fish in a quarantine tank can prevent disaster.  Setting up a holding portable pond allows the fish to be observed for parasites, bacteria infections, or fungus.  It can provide opportunity to feed the new fish medicated fish foods if it is needed without exposing existing fish to anything harmful.  Quarantine can be from 15 days to several weeks.

When quarantining fish make sure the tank is not sitting in the sun!  A small tank can heat up way too quickly.

That being said, if you are not a koi enthusiast you may be wondering if you have to do this.  You might not have a portable pond available with aerators.  Most of our customers inspect new fish and add them right in after safe transferring, but we just want to be clear that there is always a risk when adding new fish.