Yeah, we usually celebrate here when we catch our fellow newcomers before they've put fish in the tank so we can recommend a fishless cycle, but in truth, that skips over the whole sometimes lengthy thing of seeing if their filter is properly sized to the tank and goals of the tank and then whether it has the best mix of media. Its just almost impossible for any newcomer to the hobby to have the patience to go through all that long stuff and so virtually all of us just end up learning it by trial and error over the years I'm afraid, but yeah, it sure is frustrating when you've made a significant decision and later you wish you'd had more info to think about.
One good thing about your situation is that there are significant advantages to having two filters, if you can successfully fit them to the tank. A 55g at least has significant room for things to hang over the sides, although making your top accomodate it all can be challanging. With two filters you can alternate cleanings on different weekends and know that even if a cleaning caused some trouble with some of the bacteria could at most have an impact on only about half the bacteria. Likewise, a hardware failure is going to be much less of a disaster on a tank with two filters!
I know none of this may offset the impact to your wallet! But another possibility is that you could get to try one of the Pro or Pro II models and have it in a personal head to head comparison with your Classic series one. This would put you in a position to give us some good insights about maintenance between the two types and other comparisons. Also, for yourself that would help you in future filter decisions.
~~waterdrop~~
