Its not your PH if that is what you PH is. 6.2 - 6.8 from what I read is ideal for soil based grows.

What kind of soil are you using? and have you been feeding them this early in the game or have you been using plain water?

Because this sounds like a deficiency to me? Or your overfeeding.

I will add a chart to show what each symptom might be. (also got if from cannabis.com)

If you don't know.

Here is what each symbol is:

N-Nitrogen
P-Phosphorus
K-Potassium
Ca-Calcium
S-Sulfur
Mg-Magnesium
Fe-Iron
Mn-Manganese
B-Boron
Mb-Molybdenum
Zn-Zinc
cu- don't remember

Hope this help. Remember one important fact. Overfeeding kills your plants.

Is this your first grow?
pudder Reviewed by pudder on . seedling issues (color change) So I have 4 seedlings growing (1 is 9 days since planting, the others are 7). I noticed that their growth seems a little stunted compared to some photos online at their same stage. I noticed that the oldest one has slowly turned colors from a healthy kelly green into a more lime green. The leaves look basically healthy and the color change is uniform. The other seedlings are healthier looking, but I noticed their color is slowly changing as well. I took a pH reading of the soil and from the Rating: 5