probably not very long, these guys are very aggressive with each other, i had less than 1in fry in a 30in 20g long tank and now i only have 1, by the time he was barely over an inch he had killed all his siblings, and since the ad says they are already 3.5-4in they probably wouldnt get along very well at all in that size tank, but you can try and just have a big school of dither fish in there to really spread the aggression around, without aggression issues you could probably keep 3 in there until they got to 5-6in