GE Merlin Reverse Osmosis Post Filter 1244746 The GE Merlin Carbon Post Filter 1244746 is a granular activated carbon filter. It is thefinal filtering stageﾠin the GE Merlin RO System. The GE Merlin RO System Post Filter is an inline filter that provides a final polish your purified drinking water. The GE Merlin Tankless RO System Carbon PostFilter should be changed approximately everyﾠ6 monthsﾠdepending on your water quality and water usage.