Deficiency

Calcium deficiency, possibly low pH could do it too. there is non problem with Mg. If there was you won't see it for 30 days after inception. Calcium on the other hand will show up without so much lag between lack of inputs (various nutes) relative to outputs (growth)

When it comes to calcium and magnesium deficiencies, they occur because one or the other is lacking or in excess there for should be treated together. They have a symbiotic relationship in a manner. Hope this helps.

Besides all said, you may reduce light intensity for a few days. LEDs are well-known for triggering Ca deficiency more than classic HID or MH lights.

Perhaps a minor calcium deficiency based on the progressing brown spots and slight curling of some leaves. Older leaves will show some blemishes over time, so don't throw the baby out with the bath water - your diary says you're adding CalMag already. Just give a bit more on the next feed. They still look pretty healthy. so don't change too much. Good luck!