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.
You replaced all of the filter sponges in your filter? The beneficial bacteria takes home in those filters, so if you remove them, it would cause another cycle I believe. When I had a white cloudiness to my tank, it was the bacterial bloom establishing the cycle. If your filter has two sponges, I would replace one only and leave the other one. But even at that point, it would only be necessary if the filter sponge is extremely clogged with detritus that replacing it would be required. Most of the time, just a squeeze and a rinse in tank water or water that has been dechlorinated would suffice.