Cycling Your Tank & the Right Order to Add Livestock

Before a single fish goes in, your tank has to grow an invisible workforce of bacteria. It's called cycling, it can't be rushed, and understanding it is the difference between a tank that thrives and one that crashes in week three. Here's the plain version.

The nitrogen cycle, simply

Fish produce waste; waste releases ammonia, which is toxic. In a healthy tank, one type of bacteria converts ammonia into nitrite (also toxic), and a second type converts nitrite into nitrate (largely harmless in small amounts, removed by water changes). 'Cycling' is simply growing those bacteria before you add livestock, so there's a workforce ready to handle the waste.

A reliable test kit · $45
You can't see the cycle — you measure it. Testing is how you know when it's safe to add life.

The stocking order

Once cycled, add life slowly — each addition raises the bioload, and a young tank handles small steps far better than big ones:

1. Cleanup crew first. Snails and hermit crabs graze the algae that blooms in a new tank and add almost no waste.
2. One or two hardy fish. Wait a week or two, feed lightly, and let the tank absorb the new load.
3. Easy corals. Once parameters hold steady, start with soft corals — zoanthids, mushrooms, a leather.
4. More fish, then sensitive corals. Build up gradually over months, never all at once.

A new tank goes through predictable phases after cycling — the algae 'uglies' included. We map the whole arc in Your First 90 Days, and if algae does take hold, the algae guide has you covered.