Planten krijgen bladeren met plekken,iemand enig idee wat het probleem is?

I would have suggested you to add CalMag as well, because it looks like that (one if my current growing is showing that too) but like for any disease sympotms can be tricky and be something else entirely. Check this out and look if sympotms and conditions fits: https://www.growweedeasy.com/cannabis-plant-problems/calcium-deficiency If something is not right, look for other causes. Also depends when you started to add CalMag, it takes time to correct a deficiency and do not expect the brown spots to never go away, you can stop it from worsening but not regenerate the brown spots.