Hello, it is my first time growing cannabis. I planted these seeds about 3 weeks ago in soil and just noticed the lower two leaves of all three plants turned pale with brown spots/veiny patterns. I think this may be due to over watering, but it may be some deficiency since I haven't yet used any fertilizer on them except some manure that I mixed in soil before planting these. I don't know anything at all about plants so please help. Thanks.