Try right from a tap... let it sit overnight.
Also, you can lowr the hardness and PH with stuff you can get at walmart, pet stores, fish stores... not sure about the alkalinity, though. Ammonia, although dangerous will almost always be present in a non-cycled tank. It's too hard to cycle a 2 gallon
However, a 2 gallon is not too small. Some will says YES some say NO. The thing is, if you can give them warm, clean water, go for it. I suggest 2 50% water changes per week, to keep ammonia down
bettas are hardy..give them credit! =D
I prefer natural light...for the look. It brings out their natural colors, too. You can get a UV light for the tank, or have him in a decently window lit room. remember - direct sun causes algae which although is not dangerous, can look gross to us
If you can find one... look for an adjustable filter. otherwise I only suggest a bubbler to break the surface of the water.. I have a bubbler, which you can get the adjustable valve to make it gentler! You can go without a filter, too.
Welcome to the forums =D