My apologies. No elitism was intended or implied.
The original post mentioned filtration media but I don't think mentioned the intended tank and someone mentioned mechanical only and letting the plants and substrate deal with bio. I only brought up the bare bottom tank and discus as a illustration that not every person who has a tank will have substrate and plants ( or enough plants ) to deal with bio and furthered that you will need to either consider biomedia and/or be prepared to do something about it if for some reason your bio filter gets damaged/killed or is somehow otherwise inadequate such as a recently started tank. I probably did not really shape that well enough to get the reasoning behind all that across and got lost in the details. I should have not gotten caught up in the tangent though.
My goals, and practices, for my planted tanks are vastly different than my growing out tanks. I was pointing out how I deal with that side of it and don't recall saying that you HAD to do things a certain way and if I gave that impression I apologize. AFAIK - I don't own an ivory tower to pontificate from but I've been wrong before.
For an attempt to get back on topic....
Since you have bio largely covered by the plants, you can probably stick with just the mechanical media. I would probably just get some fiber floss and/or felt padding to get a decent polish on the water and go with progressively finer layers. You can get the pads for some of the other cannister filters or the cut to fit pads from the LFS if you're bored, but since you're handy enough to build the filter you can likely find MUCH cheaper alternatives at Home Depot or similar.
If you are going dutch you probably won't need much for bio anyway since the # of fish should be low but a layer of media which is not changed would be good. This could be gravel/sand or some other "dedicated" biomedia product which may be expensive but you may not need a lot of it. SOME of the biomedia products out there have "studies" showing how effective they are. I'm not sure I'd put much faith in those. As long as your biomedia won't clog, isn't somehow toxic, and you have the volume for it pretty much anything will work for it.
Some organics you can get pads for. ChemiPur or similar come to mind. They basically just absorb/adsorb the targeted chemical. i.e. ammonia or phosphate and some others. You could just stick these in above the biomedia so that you can get at them to change them out without disturbing the bio layer but below the mechanical layer so you don't waste them by clogging them up with food and other gunk.
There aren't too many ways to deal with organics other than letting plants/algae "eat" some which may prove sufficient, foam fractionation which is generally unworkable in freshwater, water changes which are generally cheap although possibly time consuming, dedicated chemical media which can be pricey but may be rechargeable, and maybe ozone which can be very effective but can also be dangerous to you and your fish if you don't take precautions and know what you're doing.
One possible way to deal with organics is if you clean/replace your mechanical media fairly. You can remove much of the stuff before it decays into the organics you want to deal with. i.e. some algae outbreaks can be fueled from the decaying leaves of plants. So if you clean out the dead leaves from the filter before they break down you can cut off that source of nutrients from them. A sponge prefilter over the intake of your filter that you clean when you feed the fish would be one way you can do this so that you won't have to break open your cannister filter too often. You might be surprised at the gunk it will collect in a day or two.
Wow, friend I like Discus too but I dont want them here ( I want to make a 55G planted with Discus in the future not now) What about my question anyone? Tom Barr?
I only want to understand how filter works more advance and how to make a balanced aquarium for tetras and similar tropical fish and a dutch scape. I want to have super clean water. Im reaching that goal in this days but still a plus in the filtration not is bad.