If they are crumbling, it is time to change them. I would be a bit wary of using new ones the same make, though, if they crumble that quickly.
I've not used the jbl micromec that Don mentioned, but I do have Eheim substrat pro in my internal. They are small balls which pack down nicely, I would seriously think about something like that rather than noodles that are too big.
Don't forget to change only about one third of the old noodles at a time with a month between each third to give time for the bacteria to migrate to the new media before removing the next batch.