New Grower What is happening to my youngster? :(

[Crusty]

I have ordered capacitive soil sensors, but they are still on the way but I'll try to look in my local shops, maybe I can find some.. Thanks for advice

 

[Crusty]

Looks like she is recovering

But now another one started to show some problems

What do you think guys is this magnesium Def with potassium def/toxicity?
Two days ago I gave him cal mag 1ml/L because on the top leaves I noticed slight yellowing by the veins. And 0.5ml/L of bloom. It's the end of first week's flowering