Brown spots 1 1/2 week into flowering

I've started noticing some brown spots on my leaves (not many, but some on top leaves, some on bottom). I just used Schultz flower boom (10/54/10) at recommended strength on my plants and I'm wondering if maybe my pH is off instead? Anyone with experience with brown spots on leaves? Not browning on the ends of the leaves, but just 1 to 2 inch spots on a few leaves per plant. I haven't tested pH ever (first grow) and I'm MG Potting soil and i've heard a lot of bad things about MG having consistency problems. Any advice?

That sounds most like Phosphorus deficiency, which you would have corrected with the ferts you gave them. Having the correct pH is important so get at least a soil pH tester asap.