Im not saying its bugs... But have u looked under the leaves????
whats the pH of the soil?
what soil are they in? what is your feeding/watering schedule so far(ppm/type of food)? when you say the soil is 6.3ph how did you determine that? Is the problem the same on the leaves that are under good light vs the ones in the shade? Is it happening on new leaves or just old leaves?
ya maybe you need food or to transplant. I figure the plant sucks what ever nutrients are in the new soil and if its been inthere long enough i usually need to feed, but if i transplant into bigger pots often enough the new soil it gets from transplanting seems like it gets thru veg without need for fertilizer till flowering.