Digital BW, The Print

Hi All, this is my first post, I have bought a printer Canon Pixma 
iP4200, and I have a problem; when I tried to print in B&W I get a 
slightly magenta copy from it, I have read if I add a little of green 
to the picture it will compensate the magenta tone and I'll get a real 
B&W.
I'm not sure about that and I didn't try it yet.
What I would like to know is if some of you already have had the same 
problem and how you solved it.
Additionally, if somebody can tell me how much is the green % that I 
should add to the picture; if that's the problem.

Thank you very much.

Sincerely,

German Bejarano