Case study. My current tank has been set up 20 months, many of the inhabitants, rocks, fish and corals came from my previous tank and even tanks before that. Over the last 20 months I have added quite a few fish and corals most corals as frags. These animals have come from a number of different LFS's here in the UK. I have never QTd any fish or coral although I do tend to dip corals. Amongst the fish I introduced directly include 4 Royal grammas, I added 2 then some months later another 2. Each time I added the RGs and within an hour or so I would notice the appearance of a few white spots and the fish would scratch on the rocks and sand no other fish would show signs of WS and in the case of after adding the second 2 the previously added established 2 would not show any signs of WS. Within 24/48 hours the white spots had disappeared and the fish had stopped scratching with no further sign of any diseases like WS appearing. I have only ever sen WS on my Royal gramma and then only for a brief period after introduction. I don't keep tangs but I do have a Foxface Regal and multibar angels along with damsels and wasses and a pair of clowns all very healthy. I have never seen a sick fish in my tank although I admit one or two have disappeared and a couple have gone carpet surfing. Do I have white spot in my tank? I would think...no expect so. It must be around 26 years now since I saw any sign of disease in any of the 10 or 11 tanks I have had in that time. I have never QTd or medicated in that time. Am I alone here in the UK who report similar? Nope I have friends who do similar to me and their fish don't get the likes of WS and they have never QTd a fish. That's just the way it is. I would never knowingly introduce a fish carrying WS but Iknow I must have done unknowingly as with my RGs which are known WS magnets and indeed showed WS on first introduction but that soon disappeared with no further signs of any such.