Before a single fish enters your tank, an invisible team of bacteria needs to move in. These nitrifying bacteria convert toxic ammonia from fish waste into nitrite, then into less-harmful nitrate. Without them, even one fish will die within days.
Start with live rock and a quality marine salt mix. Mix your saltwater to 1.025 specific gravity, let the tank run with a heater set to 78°F and a powerhead creating flow. On day one, add a small piece of raw shrimp or a few drops of pure ammonia to kick-start the cycle.
Test ammonia, nitrite, and nitrate every three days with a liquid test kit — not strips. You'll see ammonia spike in the first week, nitrite rise in weeks two and three, and nitrate appear as the process completes. Your tank is cycled when ammonia and nitrite both read zero for three consecutive tests.
Resist the urge to rush this process. Tanks stocked too early crash hard — and your fish pay the price. When cycled, add livestock gradually: one or two small fish the first week, then one every two weeks after that. Slow stocking gives your bacterial colony time to grow with your bioload.