Yep..here it is
"So here is the chemical reason this experiment was not successful.
For those of you that don't know as budlydoright predicted I got a bad case of Iron lockout due to excess copper ions.
The nutes don't swap directly with the copper, but I happen to use Citric Acid as a pH down, and that will react with copper oxide. So the citric acid keeps the copper free of oxide, the oxygen reacts with the metallic copper at the surface and oxidizes it readily.. so the cycle continues until there is no more citric acid to consume. Most pH downs will do this, some stronger acids will dissolve copper directly. This also has the side effect of neutralizing all the pH down I added, leading to pH problems.
I will message the admins to edit my first message with a warning not to use copper.
That said a stainless steel wort chiller is only $45 online, less than half the price of the cool coil product."