it almost sounds like Nutrient Disorder /lock out check out this web page ive found it has pictures of leaves with varios problems see if you can match it up...if it is a Nutrient Disorder it will probly need to be flushed

Marijuana Plants Problems - Yellow Leaves, brown spots, nutrient shortage etc.

get me some more pics asap of the changes some close ups different angles etc
let me know what you think after looking at site