wellyou upped the ec...and growing with some wattageon them.
Its just like, PLants are transpirating more, water evaporates, Nutrients stay in the plant. Now light and Heat reacts with the Plantleaves, and that is theeffect.......
You see yellowish discolored of brown spreckled leaves
So either go easier in nutes, or give them more water
BUUUT... as you are in Week 6 of flower, i wont be to concerned about the leaves....
The Plant concentrates in flower now... Burnt leaves dont hurt her too much....
But yes you can help her in going easier in Nutrients or deluting them in giving more water