OK so i working on getting a 75g setup, the tank is still being resealed i bought a penguin 350b filter to use with my marineland 250, any way back to the question
my fish is in a 20g tank it had 3 small filters runnin on it and since i had the penguin i desided to put that in my tank and took the old filter cartgres out of the small filters and put them behind the new ones in the new filter is this the correct way to swap out filters?

yep that will work. that's the way i have started my last 3 tanks. i never even experienced a mini cycle using this method either.:)