Pool Diatomaceous earth can be used safely in your diatom filter, but why would you want to use it???
It really is not necessary to use D.E. at all as the pleated cartridge is what really polishes the water.
If you do use D.E. make sure you mix the powder outside of the filter first in some tank water or you will get a huge blast of powder in the tank that will take several hours to clear!!
CM