Red stems light green tips

hey everyone...a friend of mine is tryin to grow for her first time and they are doin pretty good...they are nice and green and strong....except the leaf stems are a reddish and the outer tips of the leaves are a light green...if anyone could give me a hint that would be awesome? im not sure if they have a deficiancy or what...thx for the help!

Pictures.. and more info

Soil
Water
Ph of water and soil
Any nutes?

my cuttings are the same some redish stems and light green,

600w MH 20 inch away,

Temp 91 F
Humidity 40%
Fans
Exhaust duct
Air intake

any theoys, i wuddnt worry to much as its prolly nuffin? they growing fine