Kodiak wrote:

What is it about bettas that they need so little water. Can they live
in very acidic
low PH, water? Can they put up with more ammonia, nitrite, nitrate
than other fish?
Do they need less oxygen?

The biggest answer to the above is they have an organ called a labyrinth
that allows them to breathe air from the surface. (Neat, eh?) So they
do not solely rely upon dissolved O2 in the water for their oxygen.

Can i put ONE in a big tank full of
Goldfish?

"Can" denotes "physically possible" so the answer is "yes." ;-)

Is it a good idea? Probably not.

-D
--
"Faced with the choice between changing one's mind and proving
that there is no need to do so, almost everyone gets busy on the
proof." -Galbraith's Law