How is possible to see pearling without the water column being saturated with O2 since they will always be ready to take it if under-saturated? Plants add pure O2 to the water column via H2O splitting and the only way you can see plants do that is when the water column is satured with O2. (The process of O2 addition from plants via H2O splitting is continuous but can only be visible once the water column is satured.)

Regards
Peter Gwee