Looks like temps creeping up too high as some leaves curling up at the sides. Purple stems could indicate temperature swings or getting cold when lights off, or phosphorous deficiency (but will usually show as smokey purpling patches on the leaves as it progresses), or could just be a genetic thing.
If only the fan leaf stems are purple, it could be the strain and not temps.. I have some GDPs that have red fan stems..
Nothing..just keep an eye out..My cheapo temp/RH monitor has a remote probe and Min/Max temp reading..(($9 I think on Amazon) I only know since I grow a few strains together..Temps stay between 73-80dF days and drop to 68-72 at night ..one plant has red fan leaf stems..the others not.
I would just try and get the temperatures down when the lights are on, leaves curling in at the sides says temps are getting too high and too high temps slow growth. Wouldn't worry about the purple stems unless you start seeing smokey patches forming on your older fan leaves, it's probably due to temperatures or like buzzer777 mentioned strain.
Thanku guys im new to all this i like to do my research and find out from the greates like your self i mean ive got an additional of 16 plants which one has tried up it dead but thank you all for your help il be in touch as for the temp and ph levels Sent from my iPhone using Tapatalk