Comment: or rusty nails?

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or rusty nails?

Yellowing in aquaponics is often iron deficiency. Those with money buy chelated iron, those with a "make do or do without" attitude put a few rusty nails in the system.

This is the article that got my posting privileges revoked:
http://bklim.newsvine.com/_news/2013/05/12/18212165-dr-stan-...