purple stems and yellow leaves

hey guys running into some problems so i was gonna ask for some help
using coco coir i just flushed a plant and got a ph run off of 6.3. what do you guys think?

no idea, but i have 2 currently, one was smaller and got cold shocked, turn out looking really similar. I clipped it back and let it get a little more sleep (18/6 now, was 20/4) and it's recovering.

Nute burn?

On last pic some tips are burned, thats a sign of nute burn i think.

What are your temps at? Low temps can bring out the purple.

R u feeding it?

cal/mag maybe?

Peace
Salt

Looks like a nitrogen deficiency to me. Lots of good info here......https://www.rollitup.org/advanced-marijuana-cultivation/267989-uncle-bens-gardening-tweeks-pointers.html

what nutes are you using if any? are you using distilled or r/o water?

I'm going to go out on a ledge here and agree with Stusghost. Looks more like N deficiency than Ca or Mag.

But yeah, what are you feeding?

Im kinda having the same problem but not as much yellowing, my leaves are turning into a taco shape and my stems are srarting to turn purple but only on the top leaves. What could i do? My resrvoir ph was at about 6.5 its is now at around 5 and i added thrive alive (i think). Hopefully that helps me does anybody have any comments that can help me let me know?

thanks guys for all the input the temp goes down to maybe around 17*c on cold days while lights are off. should i throw some heaters in there? and my nutrients are at around 300ppm but ive bin giving them a break for a week though, do you think thats a bad idea? i was gonna use them next feeding. ill have to check the names i know vita max is one of them and growth plus i think then some a+b formula. and i havent used cal mag but i have it. i think i will ad 1ml per litre in next feeding if you guys dont think it will mess anything up

17 Celsius is like 62 Fahrenheit. 62 isn't dangerously low, below 50 is where you start seeing growth stop.

Cal mag plus burned the hell out of my plants at 75% of it's suggested dosage, so I never use the crap. I just put pea gravel on the surface of my soil, it helps with bugs, helps with water penetration, and the calcium in the pea gravel dissolves enough for my plant apparently.

What kind of lights are using. Do you know the color temperature/spectrum of the bulbs?