Sometimes you just notice this after a water change. This could be due to the new water having more/less O2 than your plant so osmosis occurs, which results in pearling. This is neither good nor bad. You can also see pearling if your plant has a wound on it or if you trim a plant. This is not really good, but natural with trimming.
However, if you see this on a daily basis, after lights have been on for X amount of time, this a good sign that photosynthesis is occuring and your tank has reached it's max CO2/O2 level resulting in the plants pearling. This type of pearling is a very good sign of a healthy planted tank.
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