What kind of system are you using? What line of nutes? How often do you water? At what strength/ppm? What is your pH at? What strain are you growing? What kind of lighting do you use? How close is it to your plants? What is the relative humidity? Have you seen any bugs? -- these are just a few questions that need to be answered before someone can give you an ACCURATE diagnosis.
There is no way to possibly diagnose the problem with just the given information. If there is one thing I hate; it is people who try to give advice when clearly they have no fucking idea what they are talking about.
Yellow leaves would clearly be a nitrogen deficiency, not an overabundance.. That is pretty fuckin rookie. Curling leaves indicate pH problems or over fertilization, but if there is no nute burn, then probably just Mag deficiency, or nitrogen def, OR pH problems causing some sort of lock-out. BUT, as I said there is no way to diagnose with the information provided. A lot of people act like they know what they are talking about, for whatever reason...^^ I would find someone who has posted many threads, who actually knows what they are talking about, and seems friendly to people needing help.
It will be very difficult to get someone to properly diagnose your plant without pictures. good luck, and remember to stay away from people who are full of shit!