How about a picture or more info.

Or how about checking the problem chart I posted.

Sounds like copper or manganese deficiency or surplus, or something. Since you say fertilized, I assume you are growing in dirt. If it is a fert surplus you need to flush like crazy with PH adjusted water, let the dirt almost completely dry out, then start again with 1/4 strength ferts and slowly increase until you see signs of stress again, then back off a little.