I would suggest raising the fc to about 9 for a day to see if the problem resolves. Also, an overnight chlorine loss test would be helpful.
If the cc remains or increases, or you don't pass the overnight chlorine loss test, a full Slam would probably be in order.
Note that this is assuming that the water is clean and clear with no algae. If the water quality is not very good, then a Slam is probably indicated.
In any case, I would suggest maintaining a higher fc level in general to help avoid problems.
