Filter
It works like any other filter, water and whatever from your tank is pulled thru a finger system inside the filter tank, the fingers are at the bottom and several pounds of sand is covering the fingers. The water is filtered thru the sand upwards and then returns to your tank, leaving any dirt debris, whatever at the bottom and thru-out that sand bed. the stuff that is collected stays in the sand til you backwash it out. Just like any other filter of any kind that has media that collects stuff from your tank. As long as that stuff stays in there it continues to decay and become a liquid and is gradually returned to your tank. This type of filtration is no different than any other where filter maintenance is not done frequently, if it lays in there for long enough it is eventually gonna be back in your tank. The only perfect filtration method is water change, a constant and frequent replacement of fouled water, with prefiltered clean water. So this pool filter thing is no better or worse than anything else you might do other than the fact that you are running the water thru from 100-300 # of filter sand depending on the size of the filter tank you buy.