Very difficult to diagnose with no pix, but looking at your parameters there's a few questions needing answers...
Is this a new problem, or one that you've been dealing with for a while?
How did you decide it was a manganese problem and where did the excess manganese come from?
Can you get a ph meter or kit? I'd look at the ph as possibly being a main suspect causing your un-indicated problem. (you didn't tell us what the plants are doing or what they look like)

It's usually best to keep a steady nute schedule going. Also, you may want to mention what kind of nutes you consider "good name brand stuff", as there's plenty of "good name brand stuff" that is not very good for growing cannabis. Makes it easier for those that have experience with that product line, to help you with application rates and schedules. :thumbsup: