brown dots

hey guys if you can help week 1 of flower canna newts cal mag and magnesium is added growers choice 720 LEDS flood and drain hydro rockwool why do my plants have some of these leaves?

Just wondering if anyone knows the deficiency? I have little concern over it honestly. Gotta zoom in to notice it. Brown spots or specks on 3 or 4 leafs total. I was thinking calcium, but im obviously not certain or i wouldnt be asking. Its not bugs and the setup is good. Switched to 12-12...