Newbie grower: red / purple stems

Hi guys,

Newbie grower here. I have these plants with no idea what strain they are as I grew them from random seeds. Look pretty Indica as they have big wide leaves.

They are growing very well and generally seem healthy with alot of daily growth I topped them once already with some minor trimming.
Last week I switched from 400HPS to a good quality 200W Black Dog LED.

I am currently seeing some of red/purple stems and branches. The leaves look fine with no curling or discolorations on them.

Heres some info about my setup

Tent: Jungleroom 1x1x2
Light: 200w LED blackdog full spectrum @55cm (as per manual)
Watering: once every three days, water then next water/ Canna vega on rotation
Soil: General all purpose potting mix
Ph: water around 7, soil 7.5
Light cycle: 18/6
Fans: 100mm intake and exhaust with fan speed controllers on about half.
Temps: 23c(73.4f) - 27c(78.8f)
Rh%: 53-65

I have another tent with x2 more matured plants (different strain) these are without this issue. They are on a 400w HPS light and use different soil (Canna terra professional). Everything else the same.

Thanks for your help

Dont worry about the red stems its found in Several strains.

Like @Zeeuwburger82 said certain strains have it. When in doubt look towards the leaves and new growth. If everything is healthy you’re good to go. The Leaves tell you everything you need to know.

your soil has time released ferts mixed in it so i wouldnt fertilize with bottles much if ever

Same issue, purple under LED'S fine under HPS....