Sixteen year old site that is regularly updated and popular with schools and non-profit groups. All white hat except one thing that we didn't realize mattered so much.
We use a popular link service that pays us to put text link ads on our site. We put them only in the left margin and it is clear to users that the links are not part of the content. There was no intent to deceive anyone.
Now we see that they need to have rel="nofollow" added to the tag so that they don't pass page ratings to computer algorithms that Google uses since they can't tell that they are ads.
We added rel="nofollow" and the company that pays us to put up the links say that they won't pay us unless we remove the nofollow stuff.
How long does it take for Google to notice that we added the nofollow and do we need to tell them somehow?
If it takes months to notice then that would be thousands of dollars lost for us because we are paid very well for the links.