From your description I thought at first it was a retained silver problem with your bleach (ie: not bleached enough or reusing bleach with out proper rep), but on seeing you shot of the negs I think your problem lies elsewhere. Could you have over developed it? Was the dev temp correct?
I don't have any experience with home kits but have 34 years experience with pro C41 processing. Standard machine C41 is dev 3' 15" @38C +/- 0.1C. The rest of the chemistery has a +/- 2C, you might even get away with more but I never tried it.