[SubRosa]

Flow through is where you treat your tap water to remove chlorine,raise the temp to the proper level and run it into the tank.The water which overflows instead of being filtered just goes down the drain.This can be either a continuous flow or regulated by a sprinkler timer.With this set up no filtration is necessary if you flow enough water,although most who do it use some sort of biofilter like a sponge as a back up.The only downside to this system is the initial setup expense and time,but the time saved on maintenance more than makes up for this over the long haul.

John