well just increase it gradually, do you have a feed chart from the brand of nutrients you are using?
When i bought my nutrients from my local hydro store they gave me a feed chart for every weeks progress, my first grow i used the nutrients a little leaner than recommended so ididnt see the most rapid growth.
But now i know just how much i can push the plants before they will over-react.
2 weeks does sound like long enough for a plant that far into veg to start showing these signs, i recommend that you increase the feed to atleast 1100 (lets say PPM) at this point.
When you can measure EC you want the EC to be around 1.8-2.0 at this stage of growth, pretty sure mixing nutes (atleast the brand i have) at the strength mentioned on the bottle should give you the correct readings on the truncheon.