Baby Guppies Not Growing Fast Enough!!!!!!!!!!!!!!!?

I have about 20 baby guppies in a 5 gallon tank. The temp is about 80F. I feed them first bites, crushed flakes, freeze-dried brine shrimp + bloodworms. I change the water atleast once a week. I check the water levels(they are okay). But the guppies still dont get their color till they are about 5 months old, and are about 1/2 inch at about 4-5 months. I read in a book to raise the temp to 84F, feed infurosia, and cull deformed ones, and put in a 10-20 gallon grow-out tank. Will that help?