Conditional Formatting: highlight if cell contents do not exist in range

My spreadsheet contains 5,000+ rows of text. My amounts are located in column I. I want to highlight those numbers if the corresponding account, located on the same row in column C, is not contained within a range of cells located on another sheet. My current conditional formatting formula is

=COUNTIF(Range,"<>$C:$C")

I have also tried

=COUNTIF(Range,$C:$C)<>1

Each amount will only have one account associated with it in column C, but the row location of the amounts shifts from month to month. Because of this, and due to the length of the spreadsheet, I was anticipating having to select all amounts each month (F5 -> Special...) and then insert this CF formula.

Any help would be greatly appreciated.