As for Tank Size, I think its about 3 and a half foot, and as for them getting too big, they could end up in my 5ft tank (520 litres) as of yet, my old marine is in the garage, waiting for a place to put it (new house one day), and a crack in the bottom to be fixed (doh! )
Whats the facination with Killifish? Are they quite aggressive etc? Colour?
I've considered Ciclids also, which is another option