bottom leaf death

So currently I'm growing 2 Bruce Banner (fast), 2 Purple Punch, and 1 Dutch Treat. All 5 plants are on week 4 of flower and showing signs of nutrient/PH problems. I'm using fox farms oceanic forest soil in 3.5 gallon pots, perlite at the bottom, 40% perlite through out the medium, and topdressed...