My current tank, and 60+ gallon glass was a swap out from a 55 gallon glass with terrible glass etching. When I set up the 60 gallon, I just reused the filter and media (after a tank water rinse) from the 55, a Penn Plax Cascade 700.
The filter has been doing its job, but the 700 is close to (or at) its limit in a 60 gallon, so I jacked up to a Cascade 1200. BAM!
The switch over was super easy, as the hoses and piping are the same on the 700. The extra 2 filter media trays gave me room to add a second bag of bio rings, and a bio-foam. Except the floss, all the old media from the 700 went into the 1200, which should minimize the bio-load spike. The extra media should give me a rich bio-filter, teaming with nasty little fish poop eaters.
The volume difference between the two filters was more than I expected, even with the filter 1/2 full, once I opened the taps, I lost an inch of water in the tank!
Nothing to do but test the water for a few days for safety sake, and fill up the missing water. The fish should enjoy the uber clean clean water.