Fishless Cycling vs. Fish-In Cycling: Which Should You Choose?

New aquarium owners generally choose between two approaches to establishing the nitrogen cycle: fishless cycling and fish-in cycling. The two differ significantly in both process and animal welfare impact.

Fishless Cycling

Fishless cycling uses pure ammonia or fish food as a bacteria food source, with no livestock present during the two-to-six week process. This avoids exposing fish to the toxic ammonia and nitrite spikes that occur during cycling — see our step-by-step cycling guide.

Fish-In Cycling

Fish-in cycling uses a small number of hardy fish to seed the cycle, requiring frequent water changes to keep ammonia and nitrite at survivable levels throughout the process. This method carries real welfare and health risk to the fish involved.

Why Fishless Cycling Is Generally Preferred

Most experienced hobbyists and many industry guidelines now recommend fishless cycling specifically to avoid unnecessary stress and risk to livestock during a period when water quality is inherently unstable.

Speeding Either Method Up

Adding bottled bacteria or a piece of established filter media shortens both approaches considerably, reducing the time fish (if present) are exposed to elevated ammonia or nitrite.