Thanks. Yeah, I do know better than to switch between two filters, but my fish have been sick and I couldn't decide which one to use permanently. Thanks though, joephys, that is really good advice. I don't think whispers have biological media and aquas are supposed to be changed every 3 months. I've never heard of never changing them.
Thank you also for the advice, ghinksmon. When I first took down my aqua clear the carbon had only been in it for a week and all the rest of them were fairly new as well (it was a month all the inserts were scheduled to be changed). The next week same for the whisper, but I tossed that insert. I've since switched back to the whisper (still thinking about hooking up both filters) and allowed the aqua clear inserts to dry.