Murky water in the morning?

Diatom algae is not as robust as other algaes. I've frequently seen it grow during the day when the lights were on then recede at night only to do the same thing day after day until it finally receded to nothing.

This is just pure conjecture on my part because I know next to nothing about the detailed lifecycle of marine algae, but I wonder if you're getting excessive diatom growth during the day and it gets released into the water column at night which causes the cloudiness you're seeing.

Another possibility is a bacterial bloom, but those don't tend to go away in just hours, only to repeat again hours later.