This is my first grow but i took a couple months to get all my basis covered before i started and things started off well, i have 7 plants (ak48) under two 400watt hps lights, i have a carbon scrubber and a active intake so i have good air flow and no real hot spots the temp stays at 25.5'c with an rh of 60-65, there in there 3rd week of vegging after 2 weeks as seedlings so a total of 5 weeks, Ive been using a feed/nothing/water/nothing/feed/nothing/water and so forth schedule and it seemed to be working alright( using the advanced nutrients beginner level, sensi 2part AB voodo juice, B52 and 2 others i haven't used yet), now to my problem, about a week ago some of the lower leaves on 5 of my babies right at the tips started to turn yellow this progressed to produce brown spots in the center and now the leaves dried up and died but it seems to be moving up the plants and i'm worried. Ive tried Epsom salts for magnesium deficiency and now i'm thinking maybe a potassium deficiency. i'm just looking for some input as to what it may be exactly if anyone knows, any input is appreciated thanks ,