Yellowing first leaves - CalMag ? Bugs?

Good morning I think it's a bit early to tell for sure. Don't trust those bottom single finger leaves, they usually die off eventually similar to the cotyledons. The top of the plant looks healthy. But i have come to believe in adding a calmag supplement into all of my grows...i used to have a lot of problems before i started using it. So here in the next couple weeks i would pick up the fox farm calmag and start using .25-1tsp per gallon.