How many gallons per fish?

[purplefishtail]

So I've heard the general rule of thumb is one gallon per inch of fish. I've also heard each adult discus should get 10 gallons each. I'm wondering which rule to follow in a community tank. Is 10 gallons per discus enough for a discus and a few little dither fish? Or do I have to give 10 gallons per discus plus a gallon per extra fish. It seems like neons and cardinals and other dithers don't really need a full gallon per inch because they're always schooling, but is the rule established to account for the bioload rather than the behavior of the fish. What about fish like bettas? They certainly aren't usally kept in 3 gallons of water, even if they're a 3 inch fish. Any thoughts?

[waitaki]

Hi purplefish just about your comments on Betta, I don't like the idea of keeping them in "puddle" equivalents just because they can survive in them. My betta get to live in 10 litre (about 3 gallons) and they love it and it really shows off their fins. 8-) 8-)
1 discus per 10 gallons is recommended a small school of tetras won't make much difference to the bioload; but if you try adding larger fish, well that is not going to be very healthy for your discus and is going to create extra work for you by way of regular water changes