They replace old skin with new every few weeks when they grow or when it's worn.

It looks like a thin film coming off and they usually eat it after shedding.

Excess skin shedding can be a sign of skin parasties or pollution or chemicals 

in the water.

Healthy Shedding should only take a few minutes and the frog eating it gives it extra

health as the skin contains anti-biotics and good proteins etc.