Poorly goldfish

Hi one of my goldfish is a bit poorly. He is a bit lethargic and hide under his filter but he does this a lot...last night tho, I noticed some pinkish/White cloudy patches on his dorsal fin...at first I assumed fin rot but it isn't on the edges the way it normally presents....however on his tail (it's pretty long and flowy lol) there is blood streaked through it and pink on the bottom edge. As well as that he seems to be twitching his tail in a way I've never seen before, so I'm a bit confused about this lol. He is in his own tank so my other little fish is ok. We will try to get to the shops today to get him treatment but just wondered if anyone else might know what this is?????