placed pothos plant in a hang on filter assuming it will remove nitrates (picture attached),till now no roots have been developed. It is almost close to a month since the plant stem dipped in filter. Please suggest.
I would cut off the old brown leaf joints, you need to get to a healthy "leaf node" to get good root growth. Cut it cleanly just before a green "node". You seem to have too much old "stem" to create roots.