Purple stems on some fan leaves

could be from the LED (common occurence), or it may need a bit more P ... but, if it's just the ones in strong, direct light, i'd chalk it up to LED-caused. petioles -- red or purple in stems would be sulfur. important distinction when diagnosing this. if petioles, it's P-related. If stems, it's s-related. a leaf chart with symptoms clearly displayed helps immensely. looks like you are in soil, so it's more of a guessing game.. maybe bump component withmost P and try to increase it by 5-10% (label values weighted by concentration adding up to a 5-10% increase) the less you chnage otherwise the better for determining impact while not causing other issues. give it 1-2 weeks to see impact... again, if only on top leaves closest to light, i'd chalk it up to intense LED light. but, a 5% bump isn't going to cuase any catastrophic issues if yo want to slowly test it out.

Nothing to do with nutrients or deficiencies. Could be due to colder temperatures or strain related. Some people try to get those colors by making the nights colder in the hope the buds will start purpling too. No worrys, 100% of all growers got plants with purple stems.