Filter Medium Question
I think not. The filter medium I use is very dense, so it will attract and hold very tiny particles that float around in the water. The filter medium keeps the tank water clear. I don't believe the air filter material would be dense enough to be useful as a water filter medium.
But, if you think so, give it a try and see how clear the tank water stays.
"Fear not, my young apprentice. Just change the tank water."