Its called "ick clear" now or something. LOL i cant keep track of these walmart products, but i know if you look on the back it should have the ingredients "Acriflavine, Victoria Green"
I dont think it looks like tail rot, because fungus and bacteria should not just "GROW" randomly on fishes scales like that..... It does not work like that!
There has to be an open wound for bacteria to grow on a fish like that, Nor does "fungus" actually water mould, grow like that on a fish for no reason. There has to be a wound of some sort, and since its all over the fishes skin, im thinking it has to be some sort of parasite on the outside doing damage.
I don't know about the safe on scaless fish thing, its not a product i use or reccomend alot. Its more for ick and has anti-bacterial/anti-microbial properties to it.
Should work for your situation........
It is a unique situation.
However im wondering, you said your black moor "passes away" due to some "white patches on its skin"
Was it the same kind of patches as this? Was it worse, like tail rot or under the skin lesions?
Normally goldfish dont get columnaris alot, they are natuarlly strong immune system to bacterial infections