My wizard is was caught in black tentacles and we are trying to determine the DC for my concentration check. I'm trying to cast dim. Door.
So it's (10 + CMB + 4th level spell).
We can all agree on that...
But the question is do we add a +5 the the black tentacles 25 CMD because the wizard is all ready grappled?
It states that the +5 is only for making grappling checks, not for determining CMB. Therefore, I would say that the +5 is only for making further grapple checks, like maintaining the grapple, and not applicable for the Concentration DC.
The +5 does not go to the CMD. It is only used to maintain the grapple which is what Odraude said.
You don't add the +5 (not like you are likely to make the check anyway, though - casting in a grapple is quite hard).
Note, though, that you don't use CMD to determine the concentration DC, just CMB. Still don't add the +5 though.
That's what we were thinking. Our argument being that since he was not trying to technically break the grapple the +5 to maintain the grapple wouldn't apply.