Absolutely right about P@H, we had no clue intil it was far too late. So far (2 months, 5cm long) they seem to be fine although they chase each other. If they start getting vicious we'll have to rehome them, but they're nice fish so they'll be with us as long as possible. P@H refuse to take them back.
Our platies are coldwater fish so they don't breed too much (though we've has 2 batches of fry) and the fry grow up in the adult tank to make sure it doesn't get too crowded. We'll upgraded for the surviving fry which have overcrowded the small tank but 40L is the biggest size we'll go, so i guess any fry will be given away