I took another look at the tang last night and would say it is 2 1/2 inches.
Tank has a lot of live rock; don't remember how many pounds, but it's in the range(s) of what Ive read and heard is ideal. Live sand...maybe Arag-Alive or something like that. Fluval canister 403 (or maybe it's 404?). A highly rated UV light (don't recall the brand). Seaclone skimmer (I realize that's not highly regarded). No refuge. Two Rio 600 powerheads.
I test for PH, Nitrate, Nitrite, Ammonia, Calcium, Alk, salinity, and maybe a couple of other things. Tests have basically been right on the money, although calcium is a bit low and alk a bit high.
I add
B-Ionic two-part calcium, but recently have just been adding the calc, not the alk. Also add iodine once a week.
Corals are all hardy, easy softies. Have various algae critters and a blood shrimp.
I am surprised to learn of all the concern around the mandarin fish. This may be naive, but let me ask whether this is the same fish we are talking about. Mine is the little psychedelic looking fish that sort of crawls, or flies/swims low near and around the rocks...about 2 inches. It's always seemed to do well, looks healthy, and eats well. If it is the same fish, I didn't realize they had such special needs. Maybe Ive been lucky or maybe, sadly, there'll be problems with it ahead.
Thanks, again, to everyone. I appreciate all the concern and suggestions, as well as the overall enthusiasm and rapport in this community.