I think you would find that even if you were to do a F/O tank with your 55, you would find that even within it as a F/O tank, you would start out good, but as the months ages on, you find yourself in more direr need to change these HOB to a excellent skimmer that would be better.
Your trying to be thrifty? Your not being wisely economical for this tank in the long run, you will loose so many fish one after another until you wise up that you need to be rid of these HOB filters that would only do well for you enough within a freshwater tank, but could never long term do well for your as a marine tank, specially as a reef. Best of Luck
Buddy