Help! OPK question???

China 👩🏽👦🏽👦🏽👦🏽👧🏾👼🏽🌈👶🏽 • Mommy of 7...
It's my first time using opk's and I wanted to know if the line gets darker the closer you get to ovulation. And I wanna know if you always get some form of a second line or is it ever a bfn