Filter media is the sponge or bio-balls or noodles or ceramic cylinders, anything that the water is passing through after the water enters the filter. The filter is mainly for beneficial bacteria to live in and detox the water so your fish can stay alive in a nut shell. The filter wool is just additional and not essential, in fact it causes problems by prematurely blocking well before the rest of the filter needs to be cleaned, don't use filter wool. Wool is used in some applications, but it's more of a old fashion thing, the filters of today is well past those times. There are a array of beneficial bacteria types, but ignore that just understand the basics first to keep your fish alive and feeling happy and in return full vibrant colors and behaviors.
Rough fast learn for you on the N cycle
(FISH POO, DEAD PLANT BITS, UNEATEN FOOD, DEAD FISH, ANYTHING THAT CAN BREAK DOWN) all this and dangerous toxins it produces is called AMMONIA and is consumed by BENEFICIAL BACTERIA then the beneficial bacteria releases NITRITE ALSO TOXIC AND DANGEROUS then a second type of beneficial bacteria consumes the nitrite and releases NITRATE and this is harmless at low to moderate levels, but when NITRATE levels get to high levels it to is toxic, so this is the reason for WATER CHANGES, TO KEEP THE NITRATE AT A LOW TO MODERATE LEVEL. Water changes keeps nitrate diluted at safe levels.
All filters have a good portion of biological media, it's design is to maximize surface area, eg sponge, to house maximum amount of beneficial bacteria that can be fitted into a small area.
Before you google N cycle and filtration, so you don't get confused with the terms used, firstly google--------------mechanical filter media then google biological media--- mech media cleans debris from the water mass----- and bio media creates the efficient N cycle------- the filter wool is a mechanical media
Edited by Buccal, 10 April 2012 - 02:26 PM.