Rust spots?

I noticed this on one of my plants and just a small touch of it on another. They appear to be small circular rust colored spots. I know these pictures don't do much justice, thats an ipod for ya. Any thoughts?

-Watered every other day since birth (I add perlite). At current state each gets 5 cups of water every other day.
-General Hydroponic Organic Veg & Calmag last week of veg, then moved to Bloom & Calmag
-Only gave nutrients every other watering. After a couple weeks noticed a purple patch on another plant and decided to cut the nutrients and go back to only water
-Currently in week 4 of flower

I have an idea of what the issue might be but looking for some input.

pardon the bump, thoughts?

your pics are not good enough to let us make a informed decision . but I suggest looking at these web sites I know they will help.
http://www.420magazine.com/forums/problems-pests-disease-control/81275-cannabis-plant-pest-problem-solver-pictorial.html
http://www.growweedeasy.com/marijuana-symptoms-pictures
usually rust spots is lack of magnesium . or the plant is locked out . but I can see the pics well .

not magnesium . calcium. is low . my typo.

agreed. thanks for your input