Purple/red stems??? Over night

Hi everyone so I went and checked on my auto blue cheese this morning and noticed that all the stems have turned purple, been researching but there’s multiple reasons why this could be happening. also on just one plant the leaves are slightly curling up I’m on day 10 and this is the size of them????

Light lunar 300watt led hung 22inches
daytime temp-24C
Night temp - 21C
Nutes canna A&B ( only second feed using this and Im using a quarter of the recommended dose)
calmag only just introduced this to the plants yesterday

Nothing unusual there; you're fine. Good luck