Need advice leaves dying

Hey guys I have 4 sativa plants growing in soil 3 and half weeks into flower nice looking buds but some of my fan leaves went brown crispy and fell off now the leaves around the buds are doing the same started yellow with brown spots went brown and crispy break into dust when touched the buds look great temp is 26 degrees humidity 40% ph is 6.5 600w light at 50 cm above plants feeding budzilla every 3rd watering getting worried with the small leaves around the bud doing this first time grower have flushed and added calimag 3 days ago but to be honest theres so many things I read on google I just don't want to do the wrong thing and ruin these as they are looking good budwise cheers guys in advance

what is the npk of the product and on every 3rd watering how much do you feed/ppm?
I had nitrogen issues while I used it too, no desire to again, good luck, dont panic grow organic

npk is 20/5/20 i am giving 2.5 ml per litre of each bottle

Lol what do u think I should be feeding