I have one in my filter for my DT should I take that out and replace it will some thing else. Sorry to "hijack your thread"
Do you have LR and sand in the tank>? if so thats your main filtration with good water movement and the the Hangon filters dont usually add a lot but can create a bacteria dependency where if you remove the filter pads you will have a small spike while the tank compensates from the bacteria that was removed,
I run a hang-on on my tank for added surface agitation with out the pad and when I need or what to run carbon I add in the filter pad for a couple of days and then remove it again.
mike