The main purpose of a frag tank is to house coral frags. When asking, ‘Do you need to cycle a frag tank?’, what you are really asking is what requirements need to be met to ensure coral frags remain healthy, and what do you need to do to make sure you will be able to sell them on? When we consider the fundamental, minimum requirement of coral in any healthy aquarium, we look at lighting, alkalinity, calcium, magnesium, trace minerals and nutrients. These requirements are non-negotiable for successful growth.