Blue tang love to hide in betweek liverock. Be it new or old. Sometime u might think tat e fish is dead. But actually they r sleepin. No need to be too alarm bro.
Bro its not jus about e gd water quality tat u can manage. Its about space limit. Its like 10 to 20 people living in one room. Bath, eat n sleep in 1room. Plz hear our advise n reduce ur fishes bro. No offend. Jus my 2cents.