Can't seem to find any actual sponge filters, well one but no replacement airstones for it. Could I use an internal filter like a Tetra Whisper 10i? Or something smaller like for a 6 gal or 3 gal, using my own filter pad as media? What are my options here? For info it is a 10 us gal tank and it will be used to rear molly, guppy and cory cats.