As I've been dealing with this it's crossed my mind that in some ways its as if I started a new cycle on my tank. I say this because I switched out my light bulbs. I had a simple T8 full spectrum then I changed it to a T8 Floramax bulb to help my plants. Then I switched out both of my filter sponges as I do once a month, then of course I added a dose of Excel. This was all done in one day and ever since then I have had this white cloud.