1000w grow. AK-47 tips turning black, help!

Hello,

We have 8 plants under a 1000w in a vented 6inch hood. The light is about 1 foot from the tallest plant. We use FloraNova bloom nutes, Bud Candy, Humic Acid and Magic Cal at a Ph of 6 and she's 3 weeks into flowering (pic taken during week 2), also she's potted in roots organic soil. The temp of the room is about 80. I flushed yesterday. The tips of the AK-47 leaves are turning black, whats wrong?
photo-1.JPG




You can see the tips of the leaves slightly turn up in this one.
AK-47 week 3.jpg
 
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