Get two filters that are rated for 75 gallons then add one more.

If you over filter your water your fish will stay healthy and the water will stay clean. If you under filter you'll run into health issues and possible dead fish and poor water conditions. So for filters a good rule to follow is to over shoot it.

you need to get one filter that can handle that amount of gallons.. it will say that on the box, usually for that big of a tank it will probably be a double filter.

YOU ARE RIGHT !!! TWO ARE ALWAYS BETTER!!

The main purpose of any filter is mostly chemical, to smaller extend biological and chemical.
The main purpose of a filter it to circulate the water. Thus adding an extra filter only increase the flow turn (i.e. number of time the entire volume of your tank is circulated hourly). For FW tank this amount should be about 10 to 15 times an hour.

So adding an extra filter does not increase you bioload capacity by double.

Simply pick one filter that is designed to handle 55 gallons. Use the rest of the money something else.

Just get a filter rated for 55 gallons. the people that make the filters know what their doing, so trust them and get what they suggest. Remember that you will always get what you pay for. So if your really concerned with your fishes health, invest in a good one.

u want to get 1 big 1 but if like in my tank with is a 50
i have 2 1 samm and 1 big coz mine gose all missty

Get a good filter for 55 gal tanks, than add atleast one in tank box filter and/or an undergravel filter.