Jack Dempsey Sick?

I woke up this morning and my Jack was breathing heavy. I recently
cleaned its tank, changed filters and added new gravel. I was told at
the store that I shouldn't have completely changed the tank. I have
had this fish for about 4 years now and have always totally cleaned
the tank but it has never acted that way. Maybe it was the fact that I
added a new filter and gravel as well. I was told that I removed all
the needed bacteria. What can I do now? I added a chemical called
cycle that adds some of the beneficial bateria back to the tank. Jack
seems to be doing better. I also put the old filter back on. Will I be
able to put the new filter back on and is that anything else I need to
be doing?