[Jaws]

So I made up 40G of new salt water to do a water change but I ended up with some orangie yelllow, almost sulfur looking, crud floating around on the top of the water this time. It's the same bucket of salt I've used the last 10 water changes without any problems, the only difference is this was the bottom of the pail. I always see crud when I make up water but I've never seen it take on color like this stuff. I always start by adding magnesium and then add salt once the Mg is totally disolved. Any suggestions?