Hello my friend, I am happy to tell you that this is not septoria like you expected and asked in your diary. This is just a calcium deficiency and easy to take care of.
You need to flush the soil with two times the pot volume in water without nutrients. Make sure that the pH is within the right range.
Let the soil dry for a couple of days and after you can continue watering like you did before but you need to add a cal-mag supplement into this feeding schedule and give this supplement once a week with feeding.
Enjoy your grow buddy!