Hey guys,

heres the facts:

Grow medium: 30%soil-30%vermiculte-30%perlite.
Week:3rd week in flower
Nutrition: Sensi Bloom Part A + B, B-52, Big Bud
Haven't flushed the medium.
400W HPS lamp.
space: 1x1x1 meter

I have been struggling keeping the humidity up. It falls down below twenty, very often. Most of the leaf tip points are curling into a "claw".

Been reading a lot about the problems, and came to figure it's most likely heat stress, Ph-issues and Calcium deficiences.

Can anybody please help? In case it is any of these, or something else. What should I do? Flush the medium with water, 2x the pot size? Here go the pics:

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