I had the same problem with mine after a few years. I determined that the inside of the black tube that runs from the reactor back to the tank had build on the inside. My feed tube was also full of build up. The build up would cause the drip to stop. Once the drip stopped and the CO2 cut on it would build up in the reator and cause bubbles. I would suggest cleaning or replacing all of your tubing.
Also, I never reuse media when I clean it out. I dump the left over and start with fresh.
Brad