Suggest Remedy For Weakness And Brittleness Of Nail

Lately my nails have been very weak and easy to tear, which makes me keep them clipped short to prevent rips; is this because of a vitamin deficiency? Also, one of my nails has become weaker than the rest, to the point that it's now soft enough to flatten out slightly at the edge; this same nail has alot of scratches and grooves on it, as well, that won't go away. What is this?