Diatomaceous Earth (DE) Powder that does not mix

Описание: I cleaned my pool filter and when I attempted to add DE powder it refused to dissolve or even submerge. I talked to the local pool store clerk who had cleaned pools for over 15 years and he had never heard of this phenomenon. I bought a new bag of DE powder and it instantly dissolved and disappeared into the skimmer. I would love to understand the chemistry here. Perhaps there is some commercial use for a hydrophobic powder.