Thanks minx , yep usually about 5-6 inches total and the min tank size would as mags suggest but you could keep 6 easily in a 180litre (i am currently) with good filtration and enough hiding places for them to occupy.
However these are only small so for now they would be quite happy within a 60litre 2 foot tank with good filtration for a fair while as long as an upgrade is going to happen