fixing a new paragraph, messes up the former when it comes to ragged lines

While learning ID I encountered a problem I cant find a solution for online.

I am trying to fix the look of paragraphs in a book I translated and try to polish, but every time I fixed one and move to the new ones, all former ones reflow and get messed up -.-.

As it is in APA style, all paragraphs are aligned left, so a lot of ragged lines to fix.

Settings

PS: Setting for ragged lines in my body text paragraph style is turned on. That is not my question here:-)

My body text settings are set to Based Style and Next style = [No paragraph style].

I assumed if I select the paragraph and work on that one, it won't affect my former...which isn't true. All the other ones I fixed, look again raggy. As textframes are linked I do understand that....but how to keep my former pargraphs pretty while fixing new ones? 

Thank you very much for any help!