my lower leaves are turning yellow
 

I started my 11 plant garden last week....my ppm is 420....my lower leaves are turning yellow...I assume it is low in magnesium and my ppm should be higher (is it?). I am growing tomatoes (sorry). My ph went from 6.1 friday to 7.2 today also. I plan to add some epsom salt in the morning and increase my ppm. I love this site and thanks for sharing your knowledge with us..........indy

Yes your ppm should be twice that and lower the pH every day (if you have to) to keep it in the correct range.