Lets start by saying welcome to AA, and then work bottom to top.
The most popular way to improve a tank's look is to 1st, upgrade your lighting and add more live rock followed by corals. The mini reef is very nice looking and interesting to look at as it's teeming with life. If your livestock says no to an actual reef, just adding colorful rock will make it more interesting to look at and also provide hiding places for your fish. Fish with hidey holes are less stressed, and less stressed fish are healtier and more colorful.
76 snails and crabs in what I'm assuming is a 55g tank... wow that's a lot of crabs and snails. You will need a lot of extra shells laying around for the crabs, otherwise they'll off they're neighbors to get into bigger shells. And there is possibly a food shortage, so canabilsm wouldn't be out of question.
Frozen brine can be ok, as long as the shrimp themselves are gutloaded or in other ways improved. General consensus is that brine shrimp are like eating ice cubes, you'll get full and starve at the same time. A mixed diet will provide better long term health. On the other hand, I know people with succesful mine reefs who feed nothing other than brine and plankton. I would assume most major feed companies improve their shrimp before shipping. You didn't list your livestock, but I've yet to have a fish refuse any type of frozen (not flake and exluding mandarins) food I've chosen to feed. You can mix some garlic juice in with the food and it will generally trigger a feeding response from most fish as deep in their souls they're all italian. Hell, I eat all kinds of stuff once it's been sprinkled with garlic
Also, garlic tends to boost their immune function.
Itchy fish usually means ich or other skin critters. You should be able to see little white spots on him. It's usually easier to see them on translucent parts like their fins. If so, qt
and treat him until he's healty. I've treated ich with nothing more than additional vitamins and garlic mixed in with their food and have yet to resort to medication. On the other hand, its hard to say from here if your fish is itchy, or just crawling under the rocks.