Preferred ratio of LR
to Gallon of aquarium is 1-2lbs/gallon! I would say with 45lbs in a 55 gallon you'll be pushing it. I have about 40 in my 29 gallon and plan on adding about another 20. Then I will be able to run "Filterless"!
You might be able to squeeze by if your running a good Skimmer and have plenty of PH
's pushing that water around, but to be safe I would suggest a little filter of some sorts. Check out the Emperor line of products, they are a decent price and supposedly one of the best filters out there!