Neither, unless you measure the level to begin with, and understand why.
Iodine is an element
Iodide is the ion form
http://www.advancedaquarist.com/2003/3/chemistry">http://www.advancedaquarist.com/2003/3/chemistry</a>
[IMG]http://www.advancedaquarist.com/2003/4/chemistry">http://www.advancedaquarist.com/2003/4/chemistry</a>