could be a few thing...we need more infor in order to help correctly..
age...nutes...lights..temps...and like Budds keeper said..PICS...could be a number of things...first start with PH...what is it? and rust spots could meen Mag deff...if thats it 1 table spoon epson salts to 1 gallon water....but please try and get some pics up...1 of the whole plant..and another of the leaf( close Up)..tahnks..take care and be safe