For some reason, my sourdough starter developed a reddish hue and a crust on top, what could it be?

Hey guys! Unfortunately I didn't think of taking pictures, but a few days ago, a very strange thing happened to my starter - I have fed it in the evening, placed it by the window, went to work, and then when I came back from work and when I went to feed it I saw it developed a thick crust on top, and the whole starter had this reddish hue, that it never had before. There was also some sort of condensation on the lid. I had placed it by the window as I usually do, covered with a cloth and a lid. What could this thing be? I have a backup thankfully, but this is strange.

It has always been fed with organic rye flour, one thing I have changed in the starter's routine is that I have started using tap water for a while. Might it be unwanted bacteria taking over?