I had a rare bit of cloudiness, with no stat changes, the other day too. In my case I pretty much assume that it was caused by a large bunch of different and odd types of plants that I brought home from the AGA conference and then tried to save, despite some of them getting really damaged in transit. I figured the excess debris from dying leaves was throwing things off balance. Water changes didn't help the cloudiness right away but after a couple days, things are crystal clear again. I still think good water changes right on through this sort of thing are important.
~~waterdrop~~