I have the light at a height of about 40 cm. The photo is taken immediately after watering. The water drains as it should. I use biobiz lite mix. I think it will be poor water quality or spoiled fertilizer.
How do you recognize spoiled fertilizer?
I've looked into your oroblem and watering is 99% the problem. First there might have been a case of overwatering where your plants roots were stuck in water for a long time causing leaves to yellow. Secondly don't water on the leaves but directly in the soil. Water stuck on the leaves can cause damage and sicknesses.
Good luck with the rest of your grow. A few amendments and your grow will be fine