after recent events of others i have changed what i thought was a good filtration setup, i thought that the more the better which still isn't bad at all. i used to aim for 10 times the tank volume of filtration per hour & i do still think this is very good, but only for mechanical filtration but now think around 5 times will be fine. taking out the left overs will reduce how much will affect the water parameters eventually so if they are taken out it must be good.
i tend to think that most of the biological filtration is done by the tank itself, the bacteria in the substrate IMO does alot more than the stuff in an external filter. when setting up new tanks i have always used existing media in the filters, existing substrate & some water from existing tanks never lost a fish after adding them on the second day, an issue arised when another member did the same except for the substrate & he had issues which makes me think that the substrate does more than i initially thought.
so i think, for a 200L tank you should have somewhere near 1200LPH (i have 2200LPH which probably isn't so important) of external filtration & at least an inch cover on the base of substrate.