First timer. Spots have me concerned.

I'm noticing some weird yellow/rusty looking spots on some leaves on one of my 4 ladies. Am I doing something wrong?! I'm using soil mixed by a reputable grow shop which claims all I need to do is water it. I've been giving it RO water with cal mag added per the bottles instruction and PHing to 6.8. Watering when the soil feels dry down an inch. I'm in a 3x3 grow tent with a viparspectra xs2000 quantum led @250w. Temperature is kept around 76F with RH around 50-65%. Any tips or advise would me greatly appreciated!

I wouldn't loose sleep over this. I'd it continues to get worse then I'd be concerned.