Fish Dying After Pond Relocation

Scenario

Pond moved to shadier spot 1 month ago. 6 comets dead; only large butterfly koi survives. Fish act fine, then surface-gasp, die days later.

Likely Causes

1. Water parameter shift: New location = different runoff, groundwater, or liner leachates. Test pH, KH, GH, ammonia, nitrite, nitrate.
2. Filter not re-established: Moving disrupts biofilter. Ammonia/nitrite spikes kill slowly.
3. Low oxygen: Shade reduces plant photosynthesis; warmer water holds less O2. Add aeration.
4. Disease from stress: Move stresses fish, triggering latent parasites/bacteria.

Action Plan

1. Test water daily for a week.
2. Add bottled nitrifying bacteria.
3. Increase aeration (air pump + stone).
4. Do 10% daily water changes with dechlorinated water.
5. Observe for flashing, clamped fins, lesions.

If Only Koi Survives

Koi are hardier than comets. Comets may have had underlying issues. Consider restocking with hardier species (goldfish, shubunkins) after stability returns.