So what I was wondering, is if a simple filter sponge or any foamy type thing made for a filter would work as tye filter media. All that matters is that theres a place for the BB to live, right? Then I could just buy any type of foam media and just cut it to size...
Yes, for the most part you have the right idea. What type of filter do you have? Not the brand, but the type such as canister, Hang on Back/Tank, internal, etc. You want to make sure that it fits inside the filter well enough that the water is drawn through it and doesn't go around it.
Yep. The filter cartridges you buy have carbon in them but you really don't need carbon.
The filters I use (AquaTech) have a regular filter cartridge which needs to be replaced when it falls apart but also a permanent sponge which is never removed or cleaned. The filter media in the link is what the replaceable cartridge is made of.
I use small internal filters in my betta tanks, and each one just takes a big block of sponge which is both the bio filter and the mechanical filter, but I could also layer some of the filter floss or foam together into a large brick and use that.
Oh also: what if I need to change falling apart filter media but theres not enoght room in the filter for the old and new media... Would I just put the new media in the filter and drop the old stuff in the aquarium?