Cal Mag issue? Rust spots in middle of leaf

[GnomishViking]

Noticed this leaf this morning, plants are just finishing week 4 flower and over all look very healthy despite two leaves that look like this. Plants a grown in Promix HP and are on a feed-water-feed schedule with a ph range of 6.2-6.5 when I water and feed. Pots get fully dried before I water. Temps, humidity and lights are all within normal ranges. I have been following my nutrient schedule and only thing I have added was bud candy with each feed. I do not think I have given any cal mag to this plant, but I use tap water, so I assume there would have been enough already.

 

[carlosescobar]

the other thing it could be is the start of led light burn . i would just take it off , in case it is a bug , and see if it appeared on another leaf.

 

[LoveGrowingIt]

It could be calcium deficiency, but it could also be caused by the light because it looks like it's near the top of the plant. Are any other leaves showing this condition?