It doesn't run subsequent iterations of i, because by the time i = i + 1 has run 20 times in your For j loop then i is greater than you've asked it to loop to at the start, so it doesn't need to run any more.

It's not actually clear, to me at least, what it is you're trying to achieve. Perhaps attach a workbook showing what your data looks like before and after and we can help more from there.

BSB