Correct me if I'm wrong but isn't Pyrex a brand name, not an actual type of glass? Similar to how a Xerox machine is a particular brand, not an actual sort of machine though people kind of blur that line. So is it just a misconception that these tanks are made of "pyrex" which really just means they are tempered glass, or are manufacturers using a registered trademark of a popular name synonymous with heat resistant glass as a marketing ploy? Either way this seems shady to me.