Small brown spots

Hey I have a grow which I'm just about to put in to flowering. Over the last few days I have been seeing small light brown spots on some of the leafs which I have now removed, I am extracting air and also have a fan going but is this due to humidity? or maybe over feeding??

cheers people

It could be.. we need more details tho.

they each are 3 weeks old and all 3 are starting to get tiny brown spots on first set of leaves. They each have 3 sets of leaves and are a couple inches tall. I have each one in a 24 oz. dunkin donuts cups and haven't fertilized yet. I'm using hyponex soil and will be tranplanting soon to 1/2 gallon containers and am switching over to Coast of Maine soil which is organic. i know it's not a nute problem. I do see some small black spots on the undersides of the first set of leaves that come off when i rub them but i don't think it's soil dust or anything. i do let the soil get pretty dry before waterng though, any help would really be appreciated.