In order to better help you diagnose your plants problems, please answer the following questions as best you can. Put the answers in a post in the Sick Plants & Problems forum; give as much detail as possible.
Are you growing designer genetics or bagseed?
Are you plants from seed or clone?
How old are your plants total?
Are your plants in flower?
How big are the plants (in height and # of nodes)?
What type of medium are you using and what is its makeup?
What size planter are they in?
Chemical or organic fertilizer?
How frequently do you water and how much do you use?
How frequently do you feed them and how much do you use?
Have you seen any bugs in your garden?
What size light are you using?
How big is the room they are in?
Do you have ventilation?