The Magnum 350 is still a viable option for filtration and should do a great job on a 55. The only problem with this filter, and all the Magnums are this way, is the lack of a good biological filter integrated into the canister. The Bio Wheel Pro 30 or Pro 60 solves this problem. I have been using a HOT Magnum with a Pro 30 on my 55g FW
tanks for more years than I can remember. It does a good job. You can run the Bio Wheels off the canister return or hook them to a separate powerhead.