Diatomatious Earth used in pools

I am currently training to be a lifeguard at the West Van aquatic center, and as part of the course we learn about cleaning and filtering the pool water. Along with gravel, sand and chemicals, one of the most common ways of filtering a pool is by using diatomaceous earth. After going through a few large particle pumps, the pool water travels through a tank that has polyethylene or stainless steel coated in diatomaceous earth which traps all the small particles.

In class we learned about the algae diatoms that have special glass-like walls called silica. When the diatoms die, their silica remains and makes a rock or powder called 'diatomite' or 'diatomaceous earth'. It is very abrasive, light and porous which makes it useful for a whole variety of things like toothpaste, cat litter, activator in blood clot studies and even a stabilizer in dynamite. However the most common use for it is as a filtration aid (mostly in pools.) Since it is composed of microscopic hollow particles, it is able to filter out small, fine objects that would normally clog other types of filters.They do such a great job of filtering that pool water only needs to be replaced once a year!