The borates in pool products are from sodium tetraborate pentahydrate while 20 Mule Team Borax is sodium tetraborate decahydrate. These are identical chemicals except for the water content. The tetraborate dissolves in water to form mostly boric acid and some borate ion.

This provides a pH buffer so lets one operate with a lower TA level that can help reduce the rate of pH rise from carbon dioxide outgassing. The borates are also a mild algaecide so can prevent some algae growth (mostly green algae, maybe black algae, probably not yellow/mustard algae).