I would have never guessed Ferric Ammonium Citrate was light sensitive. So the next time you find yourself with a semi load of FAC do not leave it in direct sunlight or it will prove to be worthless.

The above image was pulled from http://www.chemblink.com/products/1185-57-5.htm

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Also with it being light sensitive, does that mean that people who are treated for anemia cannot go outside?