Hello @koutogianos ! It might be a starting calcium deficiency or it might be just a random damage on the leaves. Sometimes when leaves touching something they make these marks ( like the seventh photo ). If you are using a good quality soil ( like bio bizz ) you don't really need to add magnesium. Most of the times ( when using a good soil ) magnesium deficiency comes from irregular watering ( especially a light under water ). Anyway just keep an eye on it. Check your watering schedule and if you notice an aggressive progretion of the problem only then add some cal/mag. Happy growing και καλα πιωματα ! 👊
Hey koutogianos, you're getting the start of a calcium deficiency, definitely add some cal mag, should be fully dialed in within five days ! good luck with that flower stretch ! 🚀