This is my second month using OPKs and 9th month TTC. My AF lasts from CD1-CD6 I just start testing on CD8 to make sure I miss nothing...

On CD8 I get quite a dark line, not positive but quite dark!

Cd9 is reeeeally light and stays this way and gradually gets darker and I get a positive OPK on around CD21

I have a 35 day cycle so ovulating on CD21 is perfectly average but my question is what is the dark on CD8 about? I'm just trying to be as informed as possible to try and sort out what's going on.

Thanks! :) here's my early CD8

And here's my positive on CD21