Successfully Relocating Koi from an Outdoor Pond to an Indoor Tank

Plan Ahead

Determine if the 90-gallon tank is temporary (until a new pond is built) or permanent. Koi grow rapidly; a 90-gallon tank is only suitable for very small juveniles for a short time. Seven koi will quickly outgrow it.

Prepare the New Tank First

If you have access to the new house, set up the tank there. Cycle it with a source of ammonia or use established biofilter media from the pond. Match temperature and water chemistry as closely as possible.

Moving Day Protocol

1. Use a large, sturdy container (cooler, trash can) filled with pond water covering the fish's backs.
2. Add a battery-powered air stone for oxygen.
3. Cover securely to prevent jumping and splashing.
4. Transport quickly; keep water temperature stable.
5. Bring as much pond water as feasible (buckets, totes). Fill the new tank with 100% pond water if possible.
6. If city water must be used, treat with dechlorinator (removes chlorine/chloramine).

Acclimation and Monitoring

Gradually replace pond water with new water over weeks. Test pH, hardness, alkalinity, ammonia, nitrite, nitrate, and oxygen in both sources. Add pond biofilter media (gravel, filter pads, bio-balls) to the tank filter to seed beneficial bacteria. Monitor ammonia daily for the first month; it will spike as the biofilter establishes.

If New Home Isn't Ready

Leave the koi in the pond. Moving them twice (pond → temporary tank → new tank) doubles stress. Wait until the new setup is fully ready.