Looks like they are over/under watered. Generally you only want to water when the top 1 inch of soil starts to dry out.
It could also be a sulfur deficiency. Sulfur is a major macronutrient for plants, but it is not mobile like nitrogen. When a plant begins running out of nitrogen, it will transfer it up from the lower leaves (hence why nitrogen deficient plants get yellow lower leaves first). However, when there is a sulfur deficiency, the top leaves and new growth become yellow first.
If you notice that the growth is stunted, you could consider supplementing with sulfur by using elemental garden sulfur, gypsum, or potassium sulfate.
More info about sulfur deficiencies here:
https://www.ilovegrowingmarijuana.com/marijuana-nutrient-deficiency-sulfur/