RQS quick one auto

I love this plant, living upto its name. learnt a lot from my royal dwarf, less nutes at the start and less defoliation. This girl is loving it! Getting a nice cola from the top and seeing full of trichomes, and the lowest side shoot is hopefully gonna fill into a nice cola, the rest of the internode are starting to fill in aswell, hopefully get a nice little harvest from this. 2 days later, suddenly see rusty spots on some of the leaves, gave it a rub nothing came off so assumed its not funghi. Bought some organic molasses to see if its a deficiency, hopefully will see results soon. still not seeing any change anyone know what it could be?