Leaves turn brown all of a sudden

I found this which shows the same symptoms on pics in the link: https://www.growweedeasy.com/cannabis-flowering-stage#cannabis-flowering-week-1-3: “As your plant continues through the flowering stage, it’s normal to see a few yellow or discolored leaves near the bottom of the plant, especially in the places where the leaves are no longer getting light. This isn’t anything to worry about if it’s just a few leaves as the plant is putting its energy to the top of the plant and the buds.“

I’m watering them when they are getting dry, waiting to not overwater them. I haven’t added anything to the water yet since I read the biobizz soil has enough nutrients, but I will add some now. Thanks!