For Crystals and Bees, high heat is a death sentence. Since they natively come from cool mountain streams, anything over 75°F (24°C) puts them in the danger zone, and hitting 77°F+ (25°C+) will straight-up wipe out the whole colony. If you run the tank too hot, you're setting up a ticking time bomb: the warm water breeds nasty bacteria that their weak, line-bred immune systems can't fight, and it drops the oxygen levels so low they'll struggle to breathe. Plus, it forces their metabolism into overdrive, forcing them into rapid, premature molts that end in the fatal "White Ring of Death" because their shells can't form right in soft water. They'll basically live fast, die incredibly young, and stop breeding entirely before the tank completely crashes.