Was da los

Hello, looks like magnesium to me too. But it's important to know which soil you're using, as it could also be related to the pH value. If it's organic soil, then I think magnesium. Try spraying it with Epsom salt and get yourself a CalMag product. Often, tap water isn't very rich in magnesium. If it's mineral, it could also be related to the pH value or a lockout. But I lean towards magnesium.

I suggestv you visit the "Mandala Seeds" website and read their "grow guides"........it has a great amount of excellent imformation, especially with European products, (also North American) and has super knowledge explained easily for new growers.

BioBizz soil? Usually, with less than perfect water, you have a 99% chance of a Cal/Mag problem. I've seen many reports where it usually happens starting from the 4th week.