You can test a cell for being empty (=blank) using =ISBLANK(cell reference). Result is either TRUE of FALSE.
However when your test cell should be the cell with a new value, you create a loop and the function doesn’t work.
This means you need you need something else. What is not possible to say because I don’t know your spreadsheet and your application,
The only chance I see is to use a macro but this may only run once. Otherwise the result will be changed again based on the modifications made during the first run.
Think also about the reason for entering the 0 into the cell you want to test for blank. Maybe you can find a solution here.