I would suggest that you cut up the old one- shake out the carbon-and add it in with the new one. No need to change every month-just rinse with tank water. I'd just add the used one in with the fresh one and not change them out often. Always keep an older one in there if you replace the filter so you will always have seeded material in the filter.
I have the aqua clear and like them much better because there isn't any filter media to change. The sponges last for years-just rinse with tank water and it has bio media to grow your bb on. I love them. I have 2 110's, (3) 70's and a 50.