This morning I noticed a grey spot on the tail of one of my goldies. I don't remember this being there before. It almost looks like a pimple of some sort. Could it be a fluke? I've attached a video below. There is also a patch of grey at the very end of the tail fin that was not there before and I'm not sure if this is a normal colour change? Behaviour is normal and looks otherwise healthy. Any thoughts as to what this might be? EDIT: Here are some stills, the video qual