Hey Snapple, welcome to ftf. We are pleased you have joined our friendly informative group. Absolutely NOT. A 55 is a great size to begin with. Think about it this way, the more volume of water the less likely something small going wrong can have a large effect. In a smaller tank is does not take much of an error to become devastating. Make sense? As far as the shark question, well I can't help much there. They can be aggressive, depends on how big the particular species gets. I would research for possible tank companions, pick a few and return for specific questions. I am sure someone here will be able to help.
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200 Amazon
Discus, Angel, Rummy Nose
Nano
2 Percula Clowns, 1 Chromis