Yeah, none of those fish will work in a 30g, really. The mandarin can technically fit, but unless its trained to eat frozen or pellet, it'll quickly eat all the pods
in a tank that small and then starve to death. All the other fish need much bigger tanks. There may very well be videos of small tanks with tangs in them, but that doesn't mean that tank is still doing well now. That could be a brief snapshot of how the tank looked that particular day. Tangs get ich very easily if stressed, and the. All the fish will get it and could wipe out the whole tank. Tangs need a lot of swimming space. There are fish that would work in a 30g. Check out chalk bass, royal grammas, a six line wrasse. There are lots of gobies that would work. Check out liveaquaria.com in the nano section.