Beth, In experiencing others and myself in setting up our first tanks, our enthusiasm goes into overdrive. With all the reading and information I had, seeing a lovely fish in our LFS would put me into a deaf and dumb mode and I would have to have that fish. My errors in judgement were purchasing fish that became my pets, and they grew so large that I knew they would become stressed, and eventually with great guilt, had to take them out of their secure "homes".
For me it was failing a profoundly believedf that I would supply my fish with everything they needed. When cloudy eye and ich errupted{about a year into owning them, a RegalTang and a foxface}, treated the tank with garlic for a week, did a minor water change and that was that. But as time went on 3-4 years, the tang showed signs of stress and I had to remove him. Now, my LFS says they found it a larger tank, but did they? Had I been on this forum, perhaps I would have given it to someone who definately had a larger tank. Really, they need at least a 150 or up. I've a lot of rock taking up space and he seemed so large in my 90 gal.. Not 100.
Have witnessed a friend who started her hobby armed with all the right info., she could not stop buyiong, for a 55gal.. She so overstocked that all she has had is loss of fish and she still just can't pass up a new and beautiful species. Too many corals, too many everything. Of course she has had a few complete makeovers in her tank since. Things look to be going great for her now. Fewer of everything but really lovely fishes and critters. As is mine, except for the algea she and I have to live with and manage. We have wells, high phosphate to start out with. We only have skimmers and pumps in our tanks. Mine is appro. ten years in the running and have learned to scale down and have stopped having problems. Oh, I have a filter on the main pump in my bottom 30 gal. tank.