Why is pristine water quality especially critical immediately before and after a yabby molts?

The animal is building its entire protective layer anew and is highly susceptible to toxins

The process of molting, where the yabby sheds its hard exoskeleton to grow, places immense physiological stress on the animal as it must rapidly absorb water to expand its soft new shell. During the period immediately preceding and following the shedding event, the yabby is extremely vulnerable, lacking its primary defense mechanism against physical injury and environmental exposure. Because the animal is essentially reconstructing its entire protective outer layer, water quality must be impeccable during this time. Specifically, maintaining low nitrate levels is important because the body's resources are dedicated to rebuilding, making it incapable of effectively coping with even moderate levels of environmental toxins that it might otherwise tolerate.