Read this:
https://www.equipmentworld.com/def-contamination-and-how-to-avoid-it/
"All it takes to contaminate a 5,000-gallon tanker truck of DEF is one-tenth of a teaspoon of a metal like copper, zinc, chromium or nickel says Luke Van Wyk, owner and sales manager of Thunder Creek Equipment. If you don’t know what a teaspoon looks like, those tiny salt packets you get in a fast food restaurant hold about a teaspoon. Now imagine one tenth of one of those stirred into a tanker truck full of DEF. Other contaminants such as iron,
aluminum, phosphorous, magnesium, calcium, sodium and potassium can also ruin a tanker-full of DEF in amounts of two teaspoons or less."