Cori wrote:
We used to keep a couple comets and a black moore in a 50-gallon tank together. They seemed pop flyin' and healthy and they lived for at least ~4-5 years (we gave them to someone else when we moved). I was hoping a 10-gallon would be enough for one black moore.

I had a similar predicament where I had a betta in a small tank, he died very quickly, and I had no idea why. (He was a koi betta named Dio and now the castle he had lurks in the corner of my 20g)
If you want a good in-between size, a 20 gallon freshwater tank is relatively easy and cheap to take care of, while still being able to stock a decent amount of fish. As a general rule of thumb, you can have 1 inch, or about 1 gram, of fish per gallon of water in the tank. Smaller tanks are also easier to stress out, so can sometimes be a little tougher to maintain if you aren't experienced with aquariums. (But that's just a general statement, I don't know how much you personally know!)
You could even potentially have another male betta, and other fish. They can do very well with peaceful community fish, granted they have adequate room to move around, and none of them look too much like another male betta. I've seen them done with a lot of schooling fish, they can even serve as good fry control if you have live bearers.
I have a few Micky mouse platys and cory catfish in my tank now. They're surprisingly full of character, and a lot of fun to feed.
Shazza is right about the water issue though. You need to find out if you can really use tap water or not. At least where I am it's fairly easy to find RO water for about 50 cents a gallon, so I spend about 2 bucks a week on water. I wouldn't touch my tap though, I live on a limestone shelf and my water is hard as a rock. There are also a lot of cool tricks to avoid some other monthly fees (like filters, which can be pricey), so beyond the initial setup cost, I think having a fish tank is one of the cheapest hobbys I've had.

But I won't clog up the thread with fish talk, I hope you feel better though! Losing a betta is a lot harder than some people realize.
