So the other day I was idly wondering why sodium hypochlorite comes as a liquid and isn't available as a solid like calcium or lithium hypochlorite are. I pulled up the Wikipedia page on sodium hypochlorite, and:
Ah, okay, that explains it. Either it explodes or requires refrigeration for storage, neither of which is desirable for pool usage. Unfortunate as well, as powdered sodium hypochlorite would be amazing for pool usage if it wasn't so unstable.The anhydrous compound is unstable and may decompose explosively.[2][3] It can be crystallized as a pentahydrate NaOCl·5H2O, a pale greenish-yellow solid which is not explosive and is stable if kept refrigerated.