shouldn't be too hard to look up the O2 saturation level of water on google. Once you hit that, if the plants are still photosynthesizing, then you'll see pearling.
Tanks without CO2 usually don't photosynth. fast enough to pearl
Tanks with heavy bioloads won't pearl because the fish are using up too much O2
Remember, just because a tank won't pearl doesn't mean there's something wrong. As cool as pearling is, it's not the sole indicator of a successful tank.