Too much water, too little water, spider mites... all just guesses. Can you post a photo of the plant and a close-up of the leaves?

I second what John has said..

Do you own a magnifying glass to check for bugs under the leaves?
Do you monitor your mix and see how long it takes to dry out?
Is it really dry within the root zone since you are using a big pot?
What kind of mix do you use and what it it comprised of?
How do you know when it needs watering?

Mike