Thanks for the quick response, unfortunately this doesn't seem to be working. Could it be related to the tab? In this case it's just whitespace that needs to be replaced. So, basically any space between any two strings of numbers. (What I'm working with is a lot of numbers in a table.)
Brilliant, that did it! Was testing with an old document, it works in CC2015. Thank you!
If less than ID CS6:
If you want to replace by a ~< ["espace fine", in french typography], this is better:
or, for ID CS6+: