When I worked at the wastewater treatment plant we built a koi pond and filled it with effluent from the plant. Since we were doing this (partially) to prove how clean our effluent was we did not do any pre-treating. These were not expensive koi,
IIRC they cost $10-15 each back in the mid 90's. We didn't
acclimate, just dumped the fish in. They thrived and reproduced like bunnies!
