What is the grey dust on your swimming pool floor that easily brushed away but then comes back a day later mostly in liner crevices?

Organic debris is the grey dust on your swimming pool floor that is easily brushed away but then comes back a day later, mostly in liner crevices. It is composed of dead algae, bacteria, pollen, and other organic material that falls into your pool. Organic debris can also be a breeding ground for bacteria and algae, so it's important to keep it clean.