Is this a deficiency?

one of my last 3 plants leaves are dark in color. Plant is looking great. Could this be a type of strain it is. Normal or not. No discoloration in flowers only leaves. In ffof soil. Runoff is 620 ppm 6.4 ph. 525 ppm 6.7 ph water going in. Using well water. May have a higher iron content. I seen that may be a Molybdenum deficiency. Just wondering your guys thoughts. Strain is called mi5. From justcannabisseeds. Com Oh lower leaves look normal As can see in last picture