I wouldn't put two pair even in a tank that size. My pumilio have been set up in a 36"x36"x18" viv for years and when there were two males in the viv, I got no reproduction. Both males and females can be very territorial in pumilio and even if they are getting along, will often eat each other's egg clutches. So if you want them to reproduce, put a single pair in the largest viv possible.Randy said:I'd only put one pair of pumilio in a 16 inch cube. If you were housing them in, say, a 40 gallon breeder, then I think 2 pair would be ok.