Technically yes BUT resort first to a freshwater dip and see if it takes care of concerns not mentioned.
I feel safer using ruby rally pro which is reef safe.
IF using prazi, increase oxygen with air stone
Yes, I have used it with harlequins with success, I have found prazi safe for most species. They will let you know if they are not tolerating it, and if you are observant gives you plenty of time. If they seem to be stressing too much, just do a water change up to 25% and add carbon. Most failures of prazi pro is usually an overdose, it is very important to dose to water volume, not tank size. You can split the dose into 3 parts and dose over 12 hours if you are overly concerned; you don't want to stretch it out longer than 12 hours because the effectiveness of this drug does decrease quickly.