you don't have to put the males back in. once the guppy is pregnant, shes pregnant... like a human... except when a guppies babies come out... they eat them, the dirty buggers. you'll need to get a separation net or lots of plants for the babies to hide in and even then you'll lose the stupid ones
guppies will breed and breed and breed so seperate out the males and females if you want that to stop.
the way a female gets pregnant is males swim past and squirt semen at them... i think anyways. thats what i was told. as soon as the boy babies get their colours, remove them because they will mate with their sisters and mothers and aunties and any other female present (sometimes even platies)
good luck!!!
hayley
ps. whats your male to female ratio? you should have at least a couple of females to every male... or a single sex tank. the males harass the poor females otherwise, whos life consists of pregnancy, labour, baby eating, pregnancy, labour, baby eating, etc etc