whatever fert you use you need to be sure it has pretty much everything plants need and there's about 17 different nutrients. good potting soils provide quite a bit. the spotting really does resemble mg def, but I'm not entirely sure that's it. but I am sure that this is most likely a nute def of some kind. that golden yellow spotting looks like mg def, but if you give cal mag and you don't see improvement in a few days, it's probably not mag def, but some other nutrient. so you've made the right choice in giving cal mag but don't give a great deal of it in soil as it will stick around.
if the spotting doesn't stop or go away, then take a real close look at the ingredients of your fertilizer as it might be missing something. if so, the only way to fix that problem is to use a different fert, but be careful what you use and how much of it because some of these ferts are hot stuff; for example, in potting soil you only need to use 1/4 to 1/2 teaspoon of dynagro fert in a gallon of water. The stores usually sell this in quart bottles, which means you get a lot of it and tend to use very little of it (unless you have a huge grow).
