Help with leaf problem

Plant is about 3 weeks old and the leaves started looking like this. Any idea what caused it and how to fix it?

This looks very similar to another grow already in trouble on RIU. ...? time for a flush perhaps ..? red stems indicate poor temps at night ,...keep a temp/Rh gauge in there, general lethargic looks about the plant
to my blog: https://www.rollitup.org/blogs/blog32237-flush-baby-flush.html