Apart from numerous and diverse lower animals, corals and fish, a marine aquarium also contains countless beneficial microorganisms. The effectiveness and number of bacteria cultures and microorganisms are decisive for the biological quality of the aquarium. The addition of bacteria and microorganisms is essential in newly set up marine water aquaria as inoculation to initiate and optimise nitrification. In already established aquaria they help to maintain an optimum ratio between all the beneficial bacteria cultures. Different filter materials help to optimise the water quality in the aquarium and thus to create ideal living conditions for fish and corals.