Colin got most of the IDs, but I should add a note on the blue fish. He's a bit of a mystery; he is in the damsel family, but I don't have a solid species. I've had two of them over the years; both were accidents shipped into the same shop many years apart. They start out looking a lot like juveniles from some Amblyglyphidodon species, but they just stay like that aside from slowly loosing the big-eyed baby face. They're also very good at making patterns of spots and stripes. A lot of marine fish will have a "spooked" pattern that they show (flushed or darkened, showing stripes, etc.) but these little guys don't do exactly the same pattern every time. He shows his weird patterns when the lights are out or if I startle him. A few years back I saw a pic of another of the same that was identified as an "unidentified deepwater chromis." That's the best ID I've seen so far. From my experience, they are very nervous fish. The other fish that is in there, a pajama cardinal, is the blue fish's comfort blanket. Mr blue has to be with his buddy or he would be in constant freak-out mode. The other one I had some years back had a bangai cardinal buddy for the same reason.
I wouldn't really say that marine tanks, particularly reef tanks, are just like a freshwater one with extra minerals. Fish-only marine tanks can be quite similar, but reef tanks like this one where there are so many coral and invert species crammed in together have an ecological side that I've just never seen happen in a freshwater system. With a good reef tank, you have an intricate ecosystem in place and have to keep everything in balance from the microalgaes, worms, and weird little crustaceans all the way up through the shrimp, corals and fish. Maintenance wise, my water changes on this tank just involve pouring out the canister filters (which are full of filter feeding organisms all over the walls) to clear out debris in the bottom and refilling them with clean water. Nitrogen-based nutrients register 0 and primarily I have to worry about calcium and other trace element depletion as corals and other inverts suck it out of the water to build skeletons/shells. I run carbon to catch anything that isn't biologically uptaken as well as to mitigate chemical warfare between corals.
