Why Even Bother Cycling Your Aquarium? Cycling your tank is key to keeping your fish safe and your water stable. It helps build up the good bacteria that break down ammonia and nitrite. But you might need to cycle more than once—especially after using meds or losing power. In saltwater tanks, low oxygen can lead to bacteria making hydrogen sulfide, which smells like rotten eggs. If you catch that smell, it’s a sign to deep clean and start fresh. Staying on top of your cycle keeps your tank healt