All refer to the same thing – The Nitrogen Cycle. This cycle is what occurs naturally in the water and is what keeps the chemical balance of water at life sustaining levels for the organisms living in it. In your tank this means the establishment of beneficial bacteria in the aquarium and in the filter media that help convert ammonia to nitrite and then nitrates. To establish this bacterial growth, all you need to start is an ammonia source, oxygenated water and a surface areas they can colonize.