Re: Pearling in the morning but not in the evening?
What are your nutrient levels? You may find it interesting that I see pearling whenever I add KH2PO4, even with moderate-high PO4 available, no matter the time in the photoperiod (save for the first and last 15 minutes or so). Try dosing a few hours before lights out: if you see pearling, then it is probably nutrient related, and you can narrow down whatever runs low at the end of the photoperiod. Just a thought.
An attempt at explanation until our guru shows up: It is common to see bubbles streaming from damaged plants, be it from trimming or pinholes from deficiency or whatever. But pearling is a little different, where oxygen seeps from and clings to the leaf as long as possible before floating away. This oxygen cannot dissolve in the water column and so just clings to the leaf until physics takes over and it floats to the surface. If the enviornment is not saturated with O2, we never see these bubbles.
For example, there are many tanks with healthy plants and no visible pearling. This does not mean the plants aren't in photosynthesis.
If your tanks are streaming in the morning and not streaming at night, it is *possible* that they may be suffering minor damag by animals at night, and by the end of the photoperiod they have repaired themselves. Something similar has happened to me with clumsy loaches.
Hope this helps some.