Yea, I second Tomer on that one, 70%-80% RH are drying temperatures. You need 90%-95% to keep it going. High initial acidity, too much calcium, or over salting can also contribute to brittle dry texture. You can use less P.Roq, and this cheese may have also been nice about a month ago. It's just a bit over the hill now. Sorry to hear that... better luck next batch!