WhATS the best Discus aquarium filtration and filter media?

This is where things can get interesting and opinions can vary.  Theres a lot of opinions on discus filtration.

Most filters come with media but are easily customized.  Marketing can go a bit mad with claims on fish tank filter media.  There are three types of filter media, mechanical, biological and chemical.  These are simply things to remove other things from your water.  Thus making it cleaner.

Mechanical 

This mechanically blocks things from passing it by, so it filters (or removes) various sizes of particles or debris from the water, thus cleaning the water.  As its obstructing the flow of debris it will become blocked and need cleaning or changing regularly or it will impede flow and filter function.

Biological

This type of media provides a suitable place for denitrifying bacteria to live.  This is good bacteria that you need in your tank (see the nitrogen cycle).  The bacteria pretty much looks after itself unless you do something daft to it.  But providing somewhere for it to live is where the decision on what filter media to run come in.  Most filter manufacturers will recommend their own media for a filter,  Some very expensive filter medias make claims about their surface area, the greater the area the more space for more bacteria.  I read that 30ppi sponge was the best.  It might come down to what your prefer or can afford.

Chemical 

A vast number of resins and other filter additions are available, activated carbon will remove certain compounds from your water, other resins will absorb nitrate, ammonia and other impurities.  I have had great success with Nitrate removing resins.  These all need to be recharged or replaced so decide what you water needs and add a resin to remove it if you feel it benefits your fish.  You'll soon know if its needed or not. 

TOP TIP - Activated carbon has been shown to increase instances of HITH (Hole in the Head).  I believe it removes certain properties from the water that are better left in the water.   I would only use this for a short time after a treatment, but your better off just changing the water.