Cycling establishes the bacterial colonies that convert toxic ammonia (from fish waste) into nitrite (still toxic) and finally to nitrate (relatively safe at low levels). Adding fish to an uncycled tank is the #1 cause of new-tank fish loss - the ammonia spike kills sensitive species within 48-72 hours.
Substrate, hardscape, filter media, heater, lights. Run for 24-48 hours to confirm equipment works and parameters are stable.
Use pure household ammonia with no surfactants (Ace Hardware Janitorial Strength is the hobby standard). Test ammonia with API or Salifert kit.
Dr. Tim's One and Only or Fritz Turbo Start 900 cuts cycle time from 4-6 weeks down to 2-3 weeks. Dose per package directions.
7-14 days. Test daily. Ammonia stays at 2-3 ppm initially as the bacteria establish, then begins to fall.
As ammonia drops, nitrite rises. This phase lasts 5-14 days. Re-dose ammonia to 2-3 ppm whenever it falls below 1 ppm to keep feeding the colony.
Nitrite drops, nitrate rises. The cycle is complete when both ammonia AND nitrite read 0 within 24 hours of dosing 2 ppm ammonia.
75%+ water change to lower nitrate to 5-20 ppm range before adding any livestock.
Start with the hardiest species at 25-50% of final stocking, wait 2-3 weeks for the bacterial colony to scale up, then add the rest.