I am considering using the black filter foam for my pacman frogs but i need some questions answered first.

1. Where can i find the right foam, meaning what kind of foam do other people use for their frogs?
2. How often does it need to be changed?
3. Can i use the same piece of foam over and over again by simply wringing out the foam with hot water?
4. Are their any reasons why i should not use the foam?