My breeding set up is a little different than what a lot of serious breeders do, but it should still give you an idea. Most of the serious show breeders just use more tanks and are much more selective with their line breeds. I have a "main" tank, a fry tank and a juvenile tank for each of my lines. I pick the "best of best" juveniles and put them back in the main tank as space allows. The ones that just aren't that true to the line get culled into my "mixed" guppies. Since Im just breeding already established lines this smaller set up works for me, but if you are wanting to start a whole new line you need many, many more tanks like mistergreen alluded too.