For humans, a glass of tap water is refreshing. For a fish, it can be a death sentence. The culprit isn’t "dirty" water, but the very chemicals used to keep it "clean": Chlorine and Chloramines.
When fish are exposed to these disinfectants, they experience acute respiratory distress. Chlorine is a powerful oxidant that physically burns the delicate lamellae—the tiny structures inside fish gills that exchange oxygen. This leads to gill necrosis, where the tissue begins to die, leaving the fish gasping at the surface.
While many old-school hobbyists suggest "ageing" water by letting it sit for 24 hours, this does not work for Chloramine. Unlike standard chlorine, chloramine is a stable bond of chlorine and ammonia that does not evaporate. To truly protect your fish, a high-quality Activated Carbon filter is the gold standard, as it chemically breaks these bonds before the water ever touches your tank. This content was AI-generated, please review yourself.