FWIW, according to Anthony Calfo, sloughing can be a "sign of extreme duress. Usually comprised of mucus, it is tripped by a virulent parasitic infection, or more often by severe changes in water quality (ammonia burn, acidosis from low pH, overmedication, etc"
However, it can simply be an activity that cleans its skin of minor parasites or similar.
Mine actually started sloughing when the water quality vastly improved (nitrates significantly lowered) and he started growing a bit faster. He is about 8" now. I see him do it about once a month or so.