Been noticing some rust spots on one of the girls....

Its PK deficiency , being as your girls are in flower they need lots ok PK . So if your noticing rust coloured spots I would adjust your PK solution to be a little stronger this way you can help balance out that deficiency and make it go away faster . I would also advise tho that if your going to raise the PK that you dont feed with nutrients every feeding do it every second or third feeding , this will help prevent calcium build up on your roots preventing lock outs so your plant can absorb the nutrients that are in the medium . You also wanna keep in mind that "soil" will retain nutrients far longer then say a "soiless mix" or a "hydroponic system" so adding to much all the time will result in lock outs and nutrient burns . I hope this information helps shed some light onto your question as well as understanding the very easy solution to fix your problem to have them ladies rocking and rolling :) . -Happy Growing!