Leaf Issues...help please!

My plants are 4 weeks old. Noticed this on one plant 2 days ago. Thought it was nothing. Now seeing it on another plant as well.

I am not using any nutes! My soil is fox farms ocean forest which has plenty of nutes till flowering.

thoughts?

*bump*

this post is leaving the front page quickly =O

Let them go ahile longer and watch closely, but I don't see any reason to be worried yet! Pay close attention to water pH (6.3 to 6.5 for FFOF) and temps.