Do you have a budget? If so, get some Great White mycorrhizae from Plant Success, Roots Excelurator from House and Garden, and some Cannazym from Canna.
Let your plant soil get dry but not bone dry. On your next feeding add all 3 of those products. The Great White contains beneficial fungi that will colonize your soil and make a happier place for roots. Roots Excelurator will stimulate healthy new root growth. Cannazym helps kick start the beneficial organisms that will break down dead or rotten roots and turn them into beneficial food for you plant. Like Great White, Cannazym also increases the overall health of your root zone.
Peel off that red label on the coke bottle also. Roots do not like direct light so wrap that bottles sides with electrical tape or something that won't let light penetrate through. When the roots start showing at the bottom of the container transplant into a 2 gallon pot or a 5 gallon if you want to grow a single big plant.