hmmm if you want, try getting short finned guppies... try aiming for duller colors, or more pastel colors. If your betta is not a menace, he can be with them and they don't tend to be very nippy. I've had a few males with guppies, and only a little bit of chasing from him and that's it. Again, lots of cover is suggested =D
What I would really like is something small mid to lower tank swimmers..I like albino cories but I have gravel and still not sure if going to transfer the gravel or going for sand. Oh I decided to get a petco 6.6 bookshelf..I like that it's shallow and wide instead of a 10 that I have read may sometimes be too high.
The only problem with adding another filter, is there will be more current, which isn't geat for bettas, especially in anything under 10. More fish, less room, which in turn could cause more stress for the betta. I usually only keep shrmp in anything under 10 with a betta, 10 I have guppies, ember tetras, in 20, a lot more of different species.
Sponge filters are awesome lol. Homemade, or assembled!!
Oh another reason I forgot to mention why I'd worry having fish in with a betta under 10 gallons... Most fish are ravonous eaters and the betta may miss out LOL
That does make sense with the eating thing but now I have a whole mess of sponge filter questions, I've never used one so not sure what type of airpump to get for it or anything lol. Out of the pot into the fire.
I use Tetra Whisper 10-20 quiet, and getting an adjustable air valve, will adjust the flow. USE an aquarium sponge NOT a cleaning sponge, or get an actual sponge filter piece (ebay is where I got mine)