yellow spotting leaves!!!!!

@#*@%&$!(*!$:mad: :( :eek: ..........my leaves are yellowing and spoting real bad on one of my babies, i remember reading some where that it could be a magnesium def, but if so how do i fix, or how do i find out what caused it? i know its hard to tell without pics but any advise would be gladly taken in, also is rootien 5-5-5 indoor plant food ok to use during flowering?... it was used in the beginning of life for the girls by there first caretaker,.... but i get my fox farm stuff in three days (big bloom, tiger bloom, growbig) or should i just wait the three days and keep the norm with just ph adj water?:confused: