Purple stem

Hey, there are few reasons why things go purple. Could be because of rooms temperatures, light stress or LST. Also some strains purple and get more coloured as time goes on. Their is one deficiency that can cause some purple blushing on stems and that's Phosphorous. given your feeding amounts I doubt it is that. In some of your pictures on your diary it looks as if the plants may have a bit of light stress, It comes out as mini yellow tips on the new growth. I don't think it is Nitrogen deficiency that also shows a yellow tips as the plants are so dark green, Maybe even to much nitrogen. Side note, If you can lower your temps a bit at night and during the day if possible. 24-26c is ideal and 28max. 31 all around is hot hot with only 25% RH. But if its all you can do with what you got it will be ok. its just fine tuning the numbers. This is a good little read of why things purple as well. Could be of some insight to your situation. https://www.royalqueenseeds.com/blog-should-you-worry-about-purple-or-red-cannabis-stems-n1311 Good Luck and Happy Growing!