New Life Spectrum fish food and copper

[Zoaelite]

Besides;

http://www.healthvitaminsguide.com/minerals/copper.htm
If a natural source of copper is shell fish (which is an invert) then it's safe to assume that the shell fish is storing it in its tissues, if copper is highly toxic by itself then it must be in some sort of compound. I have a feeling it's these types of compounds your finding in the NLS.