We have a 120 gallon outdoor pond which had 3 5" koi and a 6" catfish
in it for the past 2 years. The pond had an auto-refill system
straight from tap water which was recently inadvertently turned off.
After finding this, I turned the autorefill back on slowly. I figured
maybe 25 gallons at most had evaporated before we noticed the problem.
To make a long story short, all the fish died within 24 hrs, and I
figured it was from too much chlorine shock. I took this opportunity
to totally clean the pond, and cleaned out a 1" layer of sludge on the
bottom of the pond, and I also decided to get rid of about 70 lbs of
small river rock on the bottom. I refilled the pond with tap water,
and ran the pond for a week with pumps going. I readded 2 koi, and a
goldfish which all died within 2 hours. I must have done something
very wrong for them to die so fast. What killed these fish? Should I
wait longer than 1 week prior to adding fish? I do have about 60 lbs
of large rocks in the pond, should I also add back some small rocks to
help reestablish biological filtration?