I can understand that keeping answers short only raises more questions..
But it doesn't realy matter how the system is designed or constructed and how many chambers and bells and wistles are attached in the end all do the same thing.. If it is all in one canister there can be a prefilter sponge placed before the water hits the biomedia, or the prefilter sponge is placed at the filter inlet in the tank. Or you have several canister where the first one is the prefilter and any other behind that has biomedia or chemical media etc.
The prefilter sifts out the larger particles from the water can be anything thats light enough to float around and get caught by the filter suction. Melting plant parts, little snail shells, small shrimps, fish fry you never noticed, poop, etc.. This all ends up in the prefilter and as long as it is in there i will keep breaking down (stay rotting) into smaller particles. All these smaller particles, small inough to pass through the prefilter end up in the biomedia and are broken down even further with the help of the huge bacterial colony in there. Smaller particles called nitrate, phosphate, carbon and other useable and also unuseable substances. It will never be 100% clean, even if it looks cristal clear to you it contains loads of small particles to small to see.
Those bacteria are actualy everywhere in your substrate, on your plants, the glass, the hardscape, in your hoses and in the filter, if there is moist there is bacteria. It doesn't matter how smooth a surface feels under a microscoop it is still pretty rough and looks like the grand canyon, since bacteria aren't much bigger then microscopic it is rough enough for them to grab a hold and populate that surface and even hold on to eachother. Hence you see those filamentous bacteria strains waving in the current if there are enough. There they live, eat, sleep, poop, propagate, buildup and die. What dies looses grip floats away and around and ends up in the same cycle again. This whole bacterial surface attaching to anything possible is called the biofilm everybody is talking about.. This biofilm is slimey and sticky and it collects tiny dirt particles and algae spores. This is a process that keeps going on and on, if it gets to dirty you clean it out and the moment you start up the filter again it start to repopulate again and catching particles again, since these are so tiny you wont notice the first few weeks. Till it builds up in vissible quantities and looks dirty again. Since it keeps building up and if you never clean it, it will let loos at one point en spit out into the tank.
We have to make sure the flow in the filter stays optimal and its the prefilter that will clog first with accumulating large debri.. This is the one we want to clean regularly.. If you dont the flow will finaly reduce, the prefilter stops catching dirt and everything there after will clog as well with debri. And it will finaly stop filtering. If you regularly clean your prefilter, you actualy do not need to worry about the biomedia part, leaving this well alone to it's own devices is the best thing to do. No need to distrub it. You do not even need to look at it that much. The debri you find in the biofilter compartiment also contains beneficial bacteria you want to have. You can clean it out, but it'll reduce the biological process and it needs to build up again.
It's the prefilter that needs regular cleaning and the biological media behind that only needs a check every few months to see if it isn't clogged. Just a look to be sure, but if your prefilter does it's job and you maintain it correctly, the biomedia can do years without our intervention.
If your filter capacity is enough is hard to say from this point.. It depends on several things, like how do you maintain it and how is your tank setup. Do you have a lot of bioload you need a larger capacity to work it away. All depending on that a turnover from 4 to 10 x is needed and or sufficient.. Usualy newly setup tanks are very dirty the first few weeks or months.. Lots of plants can be melting and causing a lot of debri accumulating on the substrate or float around in higher turnover tanks. This can be prevented by better husbandry, cut melting plant parts off and remove it from the tank. Syphon out larger debry from the substrate.. Once all plants are established and growing well this will reduce on it's own.. Than it comes down to how is your tank stocked, is it overstocked and do you need to feed a lot, you may need a bigger filter with more flow..
If you have a lot of debri floating around you obviously have a dirty tank.. Why remains to be seen..
