Plants shouldn't live in the same pot for that long indoors. Read my sticky about efficiency and canopy and the why you should re-pot thing in the FAQs for more of an explanation.

Your medium is old and starting to degrade. The drainage is getting worse as a result, and the buffering capacity of the lime added at the factory is used up, leading to pH drops. New pot with GREAT drainage, plus a fresh soil mix with EXTRA perlite, and you are going to be in much better shape. Don't mess with the root ball. It will be fine on its own.