An Aquaclear 110 should filter your 55 gallon tank quite nicely with that fish load. The new Aquaclear numbering system refers to the gallon size tank, whereas I think the old numbering system referred to the number of gallons per hour that ran through the filter. I think that the current Aquaclear 110 is what used to be the Aquaclear 500. I have some of each, which tells you that they don't wear out easily as the new numbering system has been used for several years.
The main filtering unit is a coarse sponge, which is easily back-flushed when dirty, and reused for years. The sponge in a 110 is about 9 inches long by 3 by 3 inches. I back-flush it by removing it from the filter, running water from a faucet in the opposite direction of filter flow, and squeezing it out repeatedly. In 1-2 minutes the filter is cleaned, but still retains its important bacteria. I have cut the sponges in half crosswise, making them easier to squeeze out as I have small hands. I rinse out the sacks of activated charcoal and bacterial media by back-flushing from a faucet. I don't replace the charcoal, allowing it to function after the first month as bacterial media.
When the sponge on an Aquaclear filter clogs and needs cleaning, it rises up due to the bottom water flow, pushing the top of the filter housing upward. This is what I use to tell me when the filter needs cleaning.
I have 2 110's running on a 75 gallon tank that has a reproducing population of 100 or so plecos (Ancistris) along with a dozen Apalachee shiners. The plecos put out a lot of waste, so one filter wasn't handling the load. I also have two 75 gallon tanks each with a 110 and a couple large sponge filters containing my wife's large Bristol shubunkin goldfish. I run smaller sponge filters on my smaller tanks that contain mainly minnows and topminnows.
Over the years , I have gradually replaced the Marineland, Aqueon, and Tetra outside power filters with Aquaclear filters because I have found the Aquaclears to last longer and to be easier to clean.
Phil Nixon