Automazar yellow leaves

This is my first grow, vegetative state went perfectly and now it started flowering 2 weeks ago and the leaves started to turn yellow... I read through the stickies and I still can't figure what it is going on.

Soil : ProMix
Fertilizers : 8-4-5 vegetable plant food (That's for veg, I have the same brand for flowering)
Watering : When my moisture meter tells me it's dry (about 2 times a week)
Pot : 3 gal
Light : 18/6
Strain : AutoMazar from Dutch Passion

hmmm to me that looks like a cal/mag deff

Where can I find that? how is it called in stores? I need to fix that quick i don't want her to die

im shure that's what its called.....im from uk so diff ere I had same prob with some of mine but as im doin organic I had to buy cal and mag and just added them to my feed....theres a spray called halo that's good 2.....as im saying u just need to add some calcium and magnesium to your grow it should sort it out......but wont help leafs that already ded ......hope this helps

Thank you very much for responding! I looked over the forums and it's cal mag or nitrogen deficiency because of acidic ph, I'll try to fix that asap