Koi pond bleach treatment

["Peter W O'Dwyer jnr" <odwyerpw at nycap_rr.com>]

Folks,
A fellow I work with has a an outdoor pond that contains some 140 Koi.  Just
the other day he noticed they were acting just a bit sluggish.  So he
thought he would add just a bid of bleach several tablespoons to clear up
what he assumed was a vile breakout of sorts.  Two or Three tablespoons of
bleach and 5 - 10 minutes later he had some 70 dead Koi with another 50
gasping for air on their sides.  He turned on every garden hose he had to
flush out the pond.  He did this for about 30 minutes.  Most of the gasping
fish pulled through.  An expensive & tragic lesson.
Peter O'Dwyer