I have vertical grooves in my nails as well... not all my nails, but my ring and middle fingers look and feel like a miniature wash board. they weren't always like this, but have been for some time now. Unlike yourself, my nails are on the soft side, but have improved their strength since I have been using DE. I have often wondered why my nails are like this... thanks for asking the question, and thanks to anyone who knows anything about this!!