I'm a newbie first time grower and 2 out of my 4 plants have died so far... I'm not sure what's killing them but I water every 3 days, I've check soil before I water and the PH too (7.0)... they are about 3-1/2 weeks old in fox farms soil and have been feeding them fox farm grow big plant food at 1/4 strengths once a week... They are under 4 CLF (about 8 inches away from lights) @ 200w each at 2800 lumens each (6500k) 24hr a day with a fan constantly on. I've attached 4 pictures of them (white widow & AK-4
any help would greatly be appreciated 
any help would greatly be appreciated 