[tang daddy]

I would not run a skimmer inside the tank with another fish while they may survive for awhile if they happen to swim by the pump one day and get sucked to the side the chances of them surviving is minimal especially if you catch it too late....I'm just going by personel experience even bigger fish can die from smaller pumps they aren't the smartest to know that open ended sucking devices are not safe.

On that note if the tank is cycled then the fish should be fine in the 55g with live rock and pumps etc. I would keep an eye on params though like nitrate and amonia. If that's the only fish in the 55g a 5 gallon wc once a week should be fine if you don't over feed.

My new set up is going to be skimmerless 48g. it will house 2-3 fish a golden rabbit a goby or jawfish and inverts like pistol shrimp, fire shrimp, anemone crabs etc, also corals. I have heard and seen positive results with going skimmerless and as long as you keep up with small wc on a small tank it should be fine.