You have me confused. Are you trying to breed them? If so you should know that most if not all bettas sold in pet stores or through dealers are too old to breed. Also, although we have all heard that a betta can survive in a quart jar, he doesn't really like to. I got my first bubble nest at 5 gallons. They are a sign of contentment as well as being ready to breed.
An undergravel filter in the type set-up you are describing is mechanical filtration only. You still need to have the chemical and biological part taken care of if you want a healthy fish or don't want to have to change fish every month. There are two links I am sending for small tank filters, neither is expensive but they both do excellent jobs. The problem is that the tank has not cycled and to the filter will take a while to cycle before you will get the best results. You also need to get a
test kit and be checking the levels for nitrates, nitrites, and
ammonia. There is information on this sites home page about cycling a fish tank for beginners. I would truly suggest you read as much as you can so there are no surprises.
Here are the links: this first one has a MINI model that I use and it fits inside the tank the flow is completely adjustable
but it takes up room. Your betta may appreciate it if you picked the second model:
http://www.drsfostersmith.com/produc...004+22768+2032
This second model sits on the edge of the tank and while I have never used it myself I have heard great things about it.
It may be a little easier to clean because you would have easier access to it.
http://www.drsfostersmith.com/produc...1&N=2004+22769
Hopefully I have given you something useful here; if I can help further please feel free to let me know. Bettas are very special to me and I spend a lot of time with them so I try to help where I can.
Welcome to the group.
Rose
