Brown spots on leaves

If they are the lowest leaves it should be a nitrogen deficiency. Nitrogen is a mobile element and therefore moves from the oldest to the youngest leaves. The plant gives priority to the highest leaves so that they receive more light, and contribute to photosynthesis more. It's a little early for you to succeed. Usually the yellowing of the leaves occurs after you have flushed the roots (at the end of the sixth week). However to be sure, don't take them off but wait to see if they turn completely yellow. in that case they will fall on their own and you will be sure it is a nitrogen deficiency