Set up everything first
Fill the tank, add a water conditioner, and run the filter and heater as normal. The bacteria live mostly in the filter media and substrate, so the filter must run the whole time.
Feed the bacteria
In a fishless cycle you add a small, measured source of ammonia (bottled aquarium ammonia or a pinch of fish food) so the bacteria have something to grow on. Bottled 'starter bacteria' products can speed this up.
Test, don't guess
Test the water every few days. You'll see ammonia rise, then nitrite rise as ammonia falls, then nitrite fall as nitrate appears. When ammonia and nitrite both read zero within a day of adding ammonia, the tank is cycled.
Liquid test kits are more accurate than strips and last much longer.
Add fish gradually
Do a partial water change to lower nitrate, then add a few fish at a time so the bacteria can keep up. Keep testing for the first few weeks.
The kit list
Picks update every day based on ratings, sales and price.
Liquid test kit
Tells you exactly when the cycle is done.
Water conditioner
Removes chlorine from tap water.
Always check a species-specific care sheet, and your vet if you have concerns. Prices and availability can change.