Kind of on the flipside of this, my local pharmacy has a well-maintained 200 gallon SW
reef. It does have algae, but from what I read, algae is an indicator that the tank can grow corals. (Which the tank has many of). I absolutely love watching that tank. They have a blue tang, a couple yellow tangs, a mandarin of some sort, 2 ocellarus clownfish, and 2 black clownfish. There is a bunch of other stuff, but I am strictly a freshie so I couldn't ID them. I must have looked like a dork, but I went in there, I just walked in, sat down in front of the tank, and left an hour and a half later. I am almost positive, though, that this tank is maintained by a business, and not by the pharmacy itself.