You might consider moving the LED grow light up a few inches, just to help prevent the symptoms from spreading (high light levels works the leaves hard, and as a result it's easier for them to get nutrient deficiencies). It looks like the symptoms are worst directly under the LED grow light, a sign the leaves may be working too hard for the environment they have now.
I think you could get a
Cal-Mag supplement and use it a few times before you start flushing. It's common to see Calcium deficiencies in coco if you don't use a supplement, so it'd be good to get for next time, too. I wouldn't go crazy with a Cal-Mag supplement if you decide to use one since you're halfway through the flowering stage, just give it to them at half strength, and follow the directions on the bottle, and stop before you start flushing.
Also, have you been
checking the pH? If you're already using nutrients, the pH being too high or low is the most common reason to see nutrient deficiencies. If you're using the hydroponic version of Fox Farm "Grow Big" (which I highly recommend over the soil version for hydro or coco), I know there's some Calcium in that already. Even if you still need more Cal-Mag, keeping the pH in the right range will also help prevent nutrient deficiencies from spreading.
You're doing great by staying on top of this! A few spots on your leaves won't hurt your buds, and your buds look like they're developing very well!