i think a 4' tank is too small. mine is in a 4' tank and its a tight fit. i think you can keep a pair in a 6' tank but i think even a lone male needs a 6' tank.
Could it yes, should you eh probably not. They are active swimmers that turn into thick tanks. A pair would do best in a 6 foot 125 and as far as dithers be prepared to replace as needed.they are awesome wet pets 90% of the time.