they are pest free but im worried bcuz they werent always purple they were all green and now this transformation is happeneing and im noticing that its affecting their growing schedule, i use to be able to get 150 cuts off each one every 2 weeks, and the number are decreasing and the rooting time is also affected , i use sweet during veg to promote faster cloning, ive noticed when giving the moms less n and some carbs with proper dome conditions rooting appears in 7 days.
Some strains purple normally, it's in their genetics. I'm guessing that's not the case here because it sounds like at least some you've grown for a while and your surprise would suggest they didn't purple any before.
Most strains will purple when exposed to cold temps or big shifts in temps. This kind of purpling isn't harmful though although low temps will slow things down and can stunt growth. I've had crops show purple stems while in veg but in flower they still produced like normal.
There is also purpling that can come about from nutrient deficiencies but that tends to affect the whole plant and not just the stems. Unfortunately I don't remember off hand which nutrient deficiency was responsible for purpling. Phospherous I think as that's what gets locked out by cold temps when cold temps cause purpling.
From everything you describe I'm wondering if maybe your grow room is getting a little cooler then normal during lights out?