leaves keep dying.. pleaaaaaase help

first grow, 4 white widows, week 5 flowering, soil, 150W HPS, biobizz grow&bloom nutrients.
you can`t really see in the pictures so i`ll describe the problem: 3 of the plants are turning yellow (all the leaves are now a light green) and the bottom leaves of all them turn yellow and die.
a few weeks ago i had a problem witch i think it was a nut burn so i took it slow with the nuts. this sunday i fed them 0.75ml/l BBgrow and 2.5ml/l BBbloom. the ph looked ok on all of the plants.
what could it be? if it is nitrogen def when should i feed them again and how much? should i wait for a week to pass? `cause they`re getting yellow and dying pretty fast.
please help. i`m a few weeks away from finish line i can`t loose them now

keep mixing grobig in your feed regularly, its crazy how much MJ loves N, but, pic 2, i see some necrosis, makes be believe you might be goin cal/mag def, and or P/K, all in all, bump your feed, and make sure your addin cal/mag to the mix, peace

thanks for the answer. i did not give them any calcium or magnesium.. just what the water has.
for mag i now i can give them epsom salts. but for calcium?

Dolomite lime has both mg and calcium

oh... perfect. thanks! i don`t know where i`ll find that but i`m on it first thing tomorrow
so should i give them nuts again and some dolomite lime right away? or should i wait for a week to pass since last feeding to avoid nut burn? sorry if i ask stupid questions but i really don`t wanna screw up

use botanicare cal mag...

you should be able to get a 40lb bag of dolomite lime from any hardware store for under $10...it's a powder so you can just sprinkle it on the top of your soil and it will get absorbed in when you water.

thank you. i hope it`ll make them better soon

apparently you can`t find dolomite lime anymore in my stupid country.. neither botanicare... i only found some Canna Calcium and Canna Magnesium in 1 litre bottles and they`re quiet expensive.
are there any other solutions? the leaves keep dying on me