Declining health

Try calmag or increase it. Keep pH in check. That's about it hopefully

Purple stems is a Mag Chlorosis , light is either too intense and/or too close. You must understand the molecular structure of the chlorophyll, just look you have 4 atoms of Nitrogen surrounding the central molecular atom Magnesium. When the magnesium is lacking the thinnest part of the plant start to capture the green spectrum and reflect purplish colors…. ( https://commons.wikimedia.org/wiki/File:Chlorophyll_a.svg#/media/File:Chlorophyll_a.svg ) This is why the plant is wilting and looks suddenly unhappy… she’s burning more Mag than she can absorb and stop photosynthesizing like at night …. Growing Marijuana is easy trust me , but it can be a deep full science believe me 😊

Over all plant is looking nice, I don't know what your feeding with but purple stems can be a sign of the plant wanting more phosphorous. Now if its deficient or just not available is the question. and I feel this might be true. I grew my one clone outside and it only started showing purple stems when it was hungry and indoors it was always purple and the grow was hurting in terms of nutrients as the brand I was demoing was bunk. Some of the pics the leaves look to be pointing downwards, almost indicating they have been overwatered. It also looks like some lighting coloration on the leaves might be a sign it would like some more magnesium. Check you feed and confirm you getting enough NPK and some secondary macros like calcium and magnesium. In veg something like 4-4-8 is descent. Cannabis loves its potassium. As for cold temps. yes they can cause some colour on the leaves to turn more purple and red, but this is normally observed when temps hit aorund 8-12c at night. Best Of Luck!

Hola. Revise su diario y tengo pensamientos. Los tallos morados son signos de estrés en su planta. El frío no es el factor más grave. Creo que su maseta o recipiente es un poco pequeño para las semanas que lleva su planta Si pensamos que es fertilización,mida el ph y el ec se su drenaje, que este en los valores de ec entre 800 y 1200ppm Y el ph entre 6 y 6.5 En conclusión creo que esta plantita mejoraría con un trasplante a una maseta de 10 litros y bajando su ph a 6. Suerte

Your plant looks healthy. Yes your stems are a bit purple but as you mentioned temperature might be the cause of that. I don't think there's anything to worry about just make sure that your light is enough distance away from the plant using a DLI/PPFD meter app. Good luck with the rest of your grow and keep it up