Yea I use the big roll not floss. You cut the piece to size. Yea not felt though.I use filter felt sheets cut to size which I think is kind of in between... I do wash and reuse them but only a few times till they get too fuzzy and then I replace. But I like that I can stack the felt pieces so I can put 2-3 in at a time and just take out the top dirty one however often I want depending on the tank's state.
I haven't noticed any issues with my water level based on the felt.
Wow! Its a roll of floss I need to get out of the heat.