The first time I killed an entire tank of fish, it wasn’t because I didn’t care. I cared too much—so much that I overwhelmed a tiny 5-gallon tank with enough fish to stock something three times its size. I still remember standing in front of that cursed rectangle, watching my prized neon tetras gasp at the surface while I frantically Googled “emergency aquarium oxygen fix” at 2 AM. Spoiler alert: there isn’t one. By morning,…