The video of the impact of the use of Nualgi on a lake in Hyderabad is available on You Tube.
This clearly shows the oxygen bubbling up, due to the bloom of Diatom Algae.
The Blue Green Algae crashed out in a couple of hours.
The lake is visibly dirtier after 2 hours, this is part of the cleaning up process.
The organic matter that had settled down on the lake bed over many years, becomes loose and floats up.
Thus the lake is fully cleaned up from the bed upwards.
The oxygen bubbling is visible for over 2 weeks.
This would be visible only in heavily polluted lakes and not in lightly polluted lakes, since the Diatom bloom would be more when more nutrients are available in the water.
The dissolved oxygen level raises steadily over a few days.
The Diatoms are consumed by Zooplankton and these by fish, so there is no residue.